Sensation & Perception Exam 2

Studies about Semantic Regularities in the Environment

1) Palmer (1975): participants shown scene (kitchen) and then asked to identify objects that were either consistent (loaf of bread) or inconsistent (mailbox or drum) w/ scene --> 80% identified bread correctly, 40% identified mailbox or drum correctly after seeing kitchen b/c scene PRIMED them to see objects consistent w/ kitchen, 2) "Multiple personalities of a blob:" Same blob is interpreted differently depending on context & orientation, not what blob itself looks like - seen as hand when near person's hand, seen as foot when near where foot would be, seen as people in city scene, etc.

Explain how blue, green, red, and yellow colors are perceived according to the trichromatic theory of color: Physiological Evidence of the Trichromatic Theory of Color

1) 3 different types of cone receptors visual pigments - for short, medium, and long wavelengths, 3) These 3 cones are activated by short, medium, & long wavelengths, 4) Differences in structure of the opsin protein causes visual pigments to respond differently, 5) S, M, & L cones best respond to different combos of light wavelengths, 6) What we perceive as different colors comes from particular combinations of these 3 types of cones firing, SEE DIAGRAM ON SLIDE, 7) Metamerism makes sense b/c if all it takes to see a color is a combo of 3 cones being stimulated, you could see same color by stimulating the same combo in a different way (ex. using 3 wavelengths adjusted to look like pure color) - to our system, yellow light and combo of green & red light both look yellow at receptor level (NOT higher level processing) SEE DIAGRAM

Anomalous Trichromats

1) 3 pigments/cone receptors but nonstandard, 2) SEE DIAGRAM: modified green or red, pigments overlap more with other pigments than with normal eyes, so colors aren't as distinct as with normal vision, 3) Can see more color than dichromats, but still less than non-colorblind eyes

Mixing Lights

1) Additive color mixture: when mixing colored lights, the reflected wavelengths are added together - ex. blue and red light combine to form purple, 2) The more lights added, the more wavelengths added until all wavelengths are represented in high amount - results in eventually seeing WHITE, 3) ex. on slide: blue light (short wavelength) mixed with yellow light (medium & long wavelengths) = white b/c all wavelengths are represented

Behavioral Evidence of Corollary Discharge Theory

1) Afterimage movement: staring at something (ex. red dot) for a while, look away and you see it (in complimentary colors) EVERYWHERE you look, looks like its MOVING - image on retina stays the same (so no IDS sent), but eyes are moving (CDS sent) - so movement of the afterimage (ex. red dot) is perceived, 2) Pushing on eye while remaining focused on one point makes image jiggle - b/c no change in image (no IDS) but muscles react to correct vision when it gets blurred by pushing on eye (CDS sent) - MOTION is perceived

What does having at least 2 pigments allow?

1) Allows us to see color: people w/ 2 or 3 cone types can see differences in colors b/c we experience a PATTERN of activity across MORE THAN ONE visual pigment, 2) RATIO of firing across different types of pigments/cone receptors allows us to distinguish between color (diff. ratios for diff. colors), 3) ex. if you have red of one intensity, both types of cones (S and L) both perceive it, but L cone perceives it better - but if red is more intense, it changes intensity of how S and L cones perceive it (both perceive it more, but L still perceives it MORE than S) - ratio of change in intensity of red between S and L cones help us know it is a diff. color as opposed to the same w/ one cone, 4) More firing w/ 3 cones so more different ratios = can see more color

Functions of Color

1) Allows us to understand color signals/info - ex. know to stop when traffic light is red, knowing banana is ripe when it turns brown (evolutionary), 2) Facilitates perceptual organization: helps us discriminate between stimuli and select stimuli - ex. color is important in berry picking b/c berries look very similar to foliage around them & color is what distinguishes berries from leaves, world is structured according to color b/c animals perceive it/use it, 3) Helps us process things easily/quickly: hard to see what common objects are when colors are changed (ex. blue banana is harder to process/identify than yellow banana)

Structural Encoding & Decoding

1) Based on the relationship between voxel activation & structural characteristics of a scene (lines, contrasts, shapes, textures, etc.), 2) Structural ENCODER is calibrated by presenting a large number of images & determining how voxels responded to specific features of each scene (line orientation, detail, & position of the image), 3) These data allowed the structural DECODER to use patterns of voxel responses to predict the structural features of the image the subject was viewing

Semantic Encoding & Decoding

1) Based on the relationship between voxel activation & the meaning or category of a scene, 2) Semantic ENCODER is calibrated by measuring the pattern of voxel activation to many images that have previously been classified into categories ("crowd," "portrait," "vehicle," "outdoor") to determine the relationship between the pattern of voxel activation & the image category, 3) Semantic DECODER can then use the pattern of voxel responses to make predictions about the type/category of the scene that the subject is viewing

Trichromatic Theory of Color

1) Color vision depends on the activity of 3 different receptor mechanisms (cones that respond best to short, medium, or long wavelengths), 2) Thomas Young had original idea & Hermann von Helmholtz refined it, 3) Eyeball couldn't be examined or dissected at the time, but the theory was correct

Behavioral Evidence of the Trichromatic Theory of Color

1) Color-matching experiments: participants given test color and asked to mimic it by adjusting 3 different wavelengths of light (adjusting knobs) - evidence of trichromatic: 3 (tri) wavelengths needed to match any test wavelength, 2) Metamerism: when 2 physically different stimuli (metamers) are perceived as identical (ex. test wavelength & certain combo of 3 wavelengths look the same), 3) If it takes 3 wavelengths to produce a color identical to the pure color, there must be 3 kinds of receptors (cones)

Mixing Colors/Pigments/Paints

1) Colors/pigments/paints = Surfaces reflecting light, not colored light itself, 2) Subtractive color mixture: when mixing colored pigments, each color pigment subtracts from the light that is reflected - less and less light is reflected as each color pigment is added --> this is why many paint colors mixed = grayish color b/c most wavelengths are absorbed, 3) ADDITIVE color mixture eventually results in WHITE LIGHT and SUBTRACTIVE color mixture results in BLACK PIGMENT

Attention

1) Definition: process of focusing on specific objects while ignoring others, 2) Mental capacity is too low to perceive all info, so we use attention to decide what to perceive, 3) Attention is well-studied but difficult to operationally define & study b/c it is intertwined with many other perceptual processes, 4) Efforts to unite theories across neuroscience, computer science, psychology, philosophy, etc. has been pretty unsuccessful - it's hard to know/agree on what attention is, 5) We do know that attention is limited (penny demonstration, moonwalking bear with basketball video)

Semantic Regularities in the Environment

1) Definition: what kinds of objects co-occur or belong b/c of function - object cooccurrence & function in a scene, 2) We process objects that are semantically consistent w/ a scene schema more easily than objects that are semantically inconsistent w/ a scene - ex. process pot in kitchen more easily than printer, 3) We infer that scenes look a certain way based on what we expect

Uneven Illumination: Orientation of Surfaces

1) Our system needs info about orientation of a surface to correctly interpret lightness differences, 2) Ex. seeing folded card makes gray half look like shadow, but seeing only a circle of same card looks like circle w/ half gray half white - no shadow

Perception of Color From a Light Source

1) Perception of color from light is associated w/ the physical property of wavelength of light, 2) What we perceive as one color is usually a combination of several different wavelengths of light - brain often can't distinguish between combined wavelengths & pure light (think they're the same color), spectroscope distinguishes between wavelengths in combinations of light that we can't distinguish (class demo)

Reasons for Color Constancy: Chromatic Adaptation

1) Prolonged exposure to chromatic color results in decreased sensitivity to those wavelengths - lush scenes look less lush/vivid as we adapt to them, ex. green in summer scenes gets duller b/c we adapt, and yellow looks brighter next to dull green, 2) Same as PIGMENT BLEACHING, but specific to cones, 3) Ex. staring at red light with one eye for a while --> cones get adapted to long-wavelength light --> decreased sensitivity to red light --> causes you to see reds and oranges viewed with the adapted eye as less saturated and bright than those viewed with non-adapted eye

Color Deficits

Most are due to cone issues

Pattern of Responding in Cones (???)

SEE DIAGRAM 1) Keep in mind: its all about the differences in firing rate of the cones, 2) Different colors are differentially absorbed by cone types, 3) Excitatory minus inhibitory signals results in final response of cones

Combining the Qualities of Color

SEE DIAGRAM: Changing up/mixing these 3 dimensions creates ~1 million colors - we can't distinguish between some of them (they look the same sometimes), but they are all different

Types of Dichromatic Color Deficiencies

SEE DIAGRAMS: 1) Protanopia: missing long wavelength (L) pigments/cone receptors (missing red cones - can't see red) - 1% of males and 0.01% of females, 2) Deuteranopia: missing medium wavelength (M) cone receptors (missing green cones - can't see green) - 1% of males and 0.02% of females, 3) Tritanopia: missing short wavelength (S) cone receptors (missing blue cones - can't see blue) - rare, 0.002% of males and 0.001% of females

Reconciling Trichromatic and Opponent Process Theories

SEE DIAGRAMS: 1) Trichromatic occurs early on in the cones (S, M, & L cone receptors/pigments) - color matching, Opponent Process occurs later on in retina, LGN, & cortex with opponent cells - afterimage & simultaneous contrast, 2) Light --> Receptors (trichromatic) --> Opponent cells (OP) --> Brain, 3) SEE DIAGRAM: M & L (green & red) cones --> go to R+G- opponent cell --> M cones (green) inhibit responding of certain bipolar (opponent) cells, L cones (Red) excite the opponent cell, SO NO RESPONSE B/C CANCELS OUT, combo M (green) and L (red) cones create yellow in A DIFF. TYPE OF CELL, which inhibits responding of B+Y- opponent cell, S cones (Blue) excite opponent cell, SO NO RESPONSE B/C CANCELS OUT, 4) If you only had L cones, would be perceived as red by R+G- or if only S cones, would be perceived as blue by B+Y- opponent cell, 4) There are opposites of all opponent cells - ex. there is B+Y- and Y+B- etc.

Perceived "Color" Depends on Illumination #1

SEE GRAPH: 1) Illumination: wavelengths of sunlight vs. wavelengths from incandescent lightbulbs (tungsten bulbs - old lightbulbs) vs. newer light-emitting diode (LED) lightbulbs, 2) Sunlight contains approx. equal amounts of energy at all wavelengths (characteristic of white light - ALL wavelengths), 3) Incandescent bulb contains much more energy/emit light at LONG wavelengths (so they look slightly yellow), 4) LED bulbs contains more energy/emits light at SHORTER wavelengths (so they look slightly blue)

Reflectance

% of light that is reflected out of a certain amount of light that hits an object - reflectance curve: shows % of light reflected at diff. wavelengths of light

Uneven Illumination

1) In our 3D world, light hits stuff differently, 2) We have to figure out if changes in appearance of stuff is due to the stuff itself or the way light hits it, 3) Reflectance Edge: Edge where the reflectance of two surfaces changes (ex. 2 diff. colors of wall paint), 4) Illumination Edge: Edge where amount of light hitting object changes (ex. shadow vs. lit part of image)

Test for Color Deficit

1) Ishihara plates: shows shapes (like numbers) in different colored dots among other colored dots, if you can't see shape it means you have color deficits - can test for diff. types of deficits through diff. kinds of images, 2) Color matching test: colorblind people don't do well on those

Dress Effect

1) Looks blue and black: looks like lots of light on a surface that doesn't reflect much (bright light around dress influences it), 2) Looks white and gold: looks like not much light on a surface that reflects a lot - brightness around image seen as shadow/isolated from dress --> different interpretations of same thing under same lighting

Types of Color Deficits

1) Monochromats: only have one kind of cone (S,M, or L) or none at all, 2) Dichromats: only 2 of 3 types of cones, 3) Anomalous trichromat: all 3 cones but one is messed up

Types of Illusory Motion

1) Motion aftereffects: viewing real motion in one direction for 30-60sec (must be at least 30sec) causes stationary stimulus to appear to be moving in the opposite direction - complimentary movement (happens w/ colors too - see complimentary color after seeing one color for a while), ex. waterfall effect: things seem to move upward after staring at downward motion of waterfall for 30-60sec. b/c prolonged viewing of waterfall's downward motion exhausts/decreases activity of neurons that respond to downward motion, so more upward motion neuronal activity remains, 2) Induced motion: movement of one (usually larger) object is interpreted as movement of another (usually smaller) object (ex. movement of clouds across moon looks like moon is moving)

Combinations of object/eye/image on retina movement that result in the perception of motion in our environment - what causes motion to be perceived?

1) Object moves --> Eye is stationary --> Image on retina appears to move (movement perceived), 2) Object moves --> Eye moves --> Image on retina appears stationary (movement perceived), 3) Object stationary --> Eye moves --> Image on retina appears to be moving (but no movement perceived b/c eye is moving), 4) Overall, this shows that motion perception can't be explained just by what's happening on the retina

Dichromats

1) Only 2 visual pigments/cone receptors, 2) We can learn how dichromats see from people who have one non-colorblind eye (all 3 cone receptors) and one eye with dichromatic color deficiency (1 missing cone receptor) - know how to describe how what they see with dichromatic eye is different than normal b/c they have both

Evidence Against V4 Being the Single Color Center in the Brain

1) Opponent neurons have been found in other areas, including V1 and IT (the form area), 2) Cerebral achromatopsia occurs alongside other deficits, like prosopagnosia (issues with processing faces)

Physiological Evidence of Corollary Discharge Theory

1) Real-motion neurons in V 3/4/5 of monkeys respond to bar moving across stationary fixation point (IDS, but no CDS) - see bar as moving, but NOT when following a fixation point across a stationary bar (IDS & CDS) - so don't see bar as moving, indicates that image on retina and eye movement are being combined (evidence for corollary discharge theory - goes with theory b/c shows that we need ONE of TWO signals to perceive movement, NOT both or neither), 2) RW (person) had brain damage to the medial superior temporal (MST) area, which eliminated CDS, so when he moved his eyes around (IDS sent), he saw motion even if there was none b/c only ever had ONE of TWO signals (IDS only, not CDS) - ex. saw wall as moving if he moved eyes b/c only IDS - made him nauseous!

Why would having only one cone result in monochromatic vision if cones are sensitive to color?

1) SEE DIAGRAM: Sensitivity/absorption curve of a single cone in this type of monochromat - it looks like the one cone would distinguish between blue/cyan and orange b/c wavelengths are different for each color and cone is more sensitive to shorter wavelengths (blue) than lower wavelengths (orange), 2) But cones are just receptive to light wavelength, not the color of the light itself, 3) Even though the pigment is less sensitive to longer (orange) wavelengths, doubling the intensity of the longer wavelengths will make the cone receptor perceive them to be the same, 4) Principle of Invariance: once a photon of light is absorbed by a visual pigment molecule, the identity of the light's wavelength is lost, 5) Monochromats can match any wavelength in the spectrum by adjusting the intensity of any other wavelength

Scene Statistics

1) Scene Statistics: probability of various things occurring in a dynamic environment affects what we attend to (like person who kept veering toward the participant is likely to do so again, so she focused more on them), 2) Study (2009): looped research area, participants walked in circle & their eyes were tracked, same confederates kept walking either towards person or avoided her each time - her visual resources allocated more to people who kept veering towards her (she fixed her attention more on those ppl based on past observations of their behavior) - probably evolutionary b/c people coming toward her could be dangerous so she focused on them more/AVOIDED THEM based on their previous behavior

How Colors are Perceived According to the Trichromatic Theory of Color

1) Short wavelength cones: short (ex. blue) wavelength activates short wavelength (S) cone receptors/pigments, 2) Medium wavelength cones: medium (ex. green) wavelength activates medium wavelength (M) cone receptors/pigments, 3) Long: long (ex. red) wavelength activates long wavelength (L) cone receptors/pigments, 4) Yellow = mixture: yellow wavelength activates medium wavelength (M) cones and long wavelength (L) cones even more than M, 5) White: white wavelength (all colors) activates all wavelength cones (S, M, & L), SEE GRAPH

Opponent Process Theory

1) Theory: color vision depends on opposing responses generated by blue or yellow and red or green - 3 mechanisms that respond positively to one color/lightness & negatively to another (Black-White+ and vice versa, Red+Green- and vice versa, & Yellow+Blue- and vice versa), 2) Originally at odds with trichromatic color theory, but we now know both are true (just talk about different levels of color processing), 3) Ewald Hering developed this theory using reports of visual experience (before we could examine the eyeball/get physiological evidence), 3) Opponent processing theory addresses higher processing (retina, LGN, cortex), while trichromatic theory addresses cone receptors in the retina BEFORE OP

Evidence for V4 Being the Single Color Center in the Brain

1) There are neurons in V4 that selectively respond to color, 2) Damage to areas of V4 result in an inability to see color - cerebral achromatopsia: issue in occipital lobe (thalamus), not eyeball itself

Monochromats

1) Truly colorblind - see no color, 2) Very rare - 10 people in 1 million, 3) Only see in shades of lightness, 4) Poor visual acuity (b/c cones have more acuity & they're missing them) but high sensitivity (b/c only rods, which are sensitive) so have to protect their eyes from light, 5) 2 types: Rod monochromacy (only have rods, which aren't sensitive to color - see grayscale), & Only one type of cone (still can't see color - see card)

Lightness Constancy Checkerboard

1) White squares have reflectance of 90% and black squares have reflectance of 9%, 2) If illumination inside the room is 100 units, white squares reflect 90 units & black squares reflect 10 units, 3) If checkerboard is in the sun and illumination is 10,000 units, white squares reflect 9,000 units & black squares reflect 900 units, 4) But even though black squares reflect much more light outside than white squares do inside, they still look black, 5) Perception is determined by REFLECTANCE, not amount of light reflected - what is responsible for lightness constancy?

Load Theory of Attention

2 key concepts: 1) Perceptual capacity: idea that a person has a certain capacity that can be used for carrying out perceptual tasks, 2) Perceptual load: amount of a person's perceptual capacity needed to carry out a particular perceptual task, 3) Low-load tasks: use up small amount of person's perceptual capacity, easy, well-practiced - leaves resources available for processing other stimuli that may be present, 4) High-load tasks: use more perceptual capacity, difficult, not well-practiced - when all or most perceptual capacity is taken, there are no resources left to process other stimuli --> if a task is high-load (using most/all perceptual capacity), you are less likely to be distracted by task-irrelevant stimuli

Types of Illusory Motion Con'td.

3) Apparent motion: motion perceived when 2 stimuli in slightly different locations are flashed with the right timing (quick enough to look like they moved - ex. hands together and then apart, 2 diff. images but looks like they moved) --> must be timed correctly (this is how animation & flip books work), video: diff. images start to be seen as movement at 8-12 frames per sec. --> apparent motion activates the SAME brain areas as real motion - makes sense b/c real motion in the world is choppy to us too, and it is integrated/combined by the brain

Uneven Illumination Illusion

A and B are the same shade but B looks lighter - partly b/c of lateral inhibition (A more surrounded by light squares = looks darker, B more surrounded by dark squares = looks lighter) AND due to correcting for shadow cast over B (looks lighter)

Corollary Discharge Theory

A comparator process induces your perception of motion if ONE but not BOTH of the signals are received: 1) Image displacement signal: signals that image on the retina has changed, 2) Motor signal (not important): signal sent to move eyes (90% of visual info goes to LGN, 10% to superior colliculus), 3) Corollary discharge signal: copy of the motor signal sent to signal that eyes have moved, 4) Comparator: goes between image displacement signal (IDS) and corollary discharge signal (CDS) - if there is an IDS but no CDS, MOVEMENT must be happening (instead of eyes just moving) and vice versa (CDS but no IDS - must be NO MOTION b/c no change in image on retina), if BOTH IDS and CDS happen - must be NO MOTION (eyes have just moved, causing image on retina to move - object must be stationary b/c it does not follow the eye as the eye moves), NEITHER CDS or IDS (if staring at object and image on retina stays the same) - object must be STATIONARY b/c neither eyes nor image changes

Chromatic Adaptation: Partial Color Constancy

After chromatic adaptation, our perception of still shifts in the presence of a color, but just not as much as it would without adaptation - eye can adjust its sensitivity to diff. wavelengths to keep color perception approximately constant as illumination changes, --> STUDY of chromatic adaptation: 1) Baseline: observer stares at green square while both observed & paper were illuminated by white light - see GREEN, 2) Observer not adapted: paper illuminated by red light, observer illuminated by white light (observer not chromatically adapted) - see REDDISH GREEN, 3) Observer adapted to red: both paper & observer illuminated by red light (observer is chromatically adapted) - see SLIGHTLY REDDISH GREEN/YELLOWISH = PARTIAL COLOR CONSTANCY b/c don't see red as much, see green more

Why do we need a mask after each image is flashed in gist demo?

After-image and sensory memory: retina holds onto images for longer than they are there, which can distort perception of the next image - the mask (gray patterned screen) wipes sensory memory by removing after-image

Saturation

Amount of white added to a hue - ex. light blue is pure blue with low saturation (lower amount of white = higher saturation)

What Happens When We Attend: #3

Attention can influence appearance: Study - 1) Fixate on dot, cue dot flashed (participants told it was irrelevant) that usually was on side with greater contrast grating if it was diff., then stimuli with grating presented, 2) Task: determine the orientation of the grating w/ the greatest contrast, 3) Results: on DIFFERENT contrast trials, cue dot didn't matter, but on SAME contrast trials, grating on the cued side APPEARED to be of greater contrast, 4) Implies that nature of presentation can change due to covert attention, not just speed of processing

What Happens When We Attend: #4

Attention can influence physiological responding: attention to objects increases the response of specific areas in the brain - Study #1: 1) Face and house images overlapped and participants told to pay attention to one of them, 2) Attention to face activated FFA and attention to house activated PPA (we discussed this) --> Study #2 - 1) Attention to locations increases the response of specific areas in the brain, 2) While fixating on center of image, participants were told to direct covert attention to a particular area, 3) This activated areas of the brain that corresponded to areas in the visual field where covert attention was directed, EVEN THOUGH they never looked directly at these places in visual field (foveal focus was on center of image), 4) Computers could predict 100% where people were directing attention, showing that covert attention was highly associated/correlated w/ brain activity, Study #3 - 1) Receptive fields in the middle temporal lobe (MLT) in monkeys shifted depending on what the monkey was attending to, 2) Shows that attention can shift the location of a neuron's receptive field

What Happens When We Attend: #2

Attention speeds responding to objects: 1) Object based attention PRECUEING experiments - cue presented (line where box would appear on AB or CD rectangle), cue off, and then target (box) presented in same or different area than cue (A, B, C, or D) - majority of trials were valid (cue matched target), 2) Participants asked to press button when target (box) appeared, 3) RESULTS: When cue and target were both A, target was processed fastest, seems like D target would be detected slowest if cue is on A b/c it is farthest away, speed of processing when cue was on A and target was C vs. B - B as target processed slightly quicker b/c A and B share object, 4) Covert attention causes enhancement to spread across objects (SAME-OBJECT ADVANTAGE), so cuing A would also direct attention to B, 5) Location (how close other points are to the pt. covert attention is focused on OR the cue) and belongingness (sharing object) are both important in whether target will be processed quickly based on where cue is, 6) SAME-OBJECT ADVANTAGE: faster responding when attention spreads within an object, even when objects are occluded (covered)

Covert Attention

Attention to stimuli without explicitly looking at it --> CANNOT be measured w/ eye tracker, but can be seen with object tracking (ex. fixating on one point while dots move around the screen and tracking the dots)

Brain Reading/Decoding

Brain activity is measured while a participant is looking at a bunch of images: 1) Person looks at images, 2) Brain activity is measured across many 3D pixels, 3) Computer program is trained to associate category of image with pattern of brain activation when person sees that image, 4) "Mind reading:" can tell what someone is thinking about by looking at brain activation pattern

Fixation

Brief pauses of directed eye gaze - can be observed with eye tracking (can use heat maps or tracking device for eye tracking)

Theory of Global Image Features

By Oliva & Torralba (2001, 1006): Helps explain why we perceive the gist of scenes so fast - Global image features: features holistically (completely/wholly) & rapidly perceived and associated with particular types of scenes - 5 features: 1) Degree of naturalness: how natural the scene is textured zones & undulating contours - more straight lines/edges = more manmade, 2) Degree of openness: how open scene is - whether or not there is a visible horizon (ex. ocean scenes more open than kitchen), 3) Degree of roughness: number of elements occurring in scene and their roughness & smoothness (ex. ocean less small elements so smoother, forest more small elements so rougher), 4) Degree of expansion: convergence of parallel lines as they get farther away - shows depth/how far away things are in scene, 5) Color: we tend to perceive color first (ex. ocean typically blue, so see something blue & assume gist of the scene = ocean)

What directs overt attention? #2

Cognitive Factors: beyond first reaction (salience), we attend to parts of a scene based on our goals/knowledge/past experiences w/ particular locations: 1) SCENE SCHEMA: observer's knowledge about what is typically contained in a scene, 2) Study: found that fixation time on item (jam jar) while locating it was similar w/ and w/ out prior exposure to the scene - probably b/c kitchen scene was similar to other kitchens that the participants had seen (past experience), so it didn't matter if people had studied the particular kitchen scene, 3) 45% of fixations happened close to intersections b/c we know (based on prior experience) that stop signs are most likely to occur at intersections, so we fixate more at intersections b/c that is where we expect to see them

New Theory About Color & Form

Color pays a role in determination of form: evidence - double-opponent receptive field neurons (these cells ONLY use color to determine boundaries of objects/stimuli), form AND color info processed in the SAME brain areas

Conclusion About V4 Being the Single Color Center in the Brain

Color perception probably occurs from activity in many parts of the brain, most of which respond to other qualities as well as color

What Happens When We Attend: #1

Covert attention speeds responding to locations (SPATIAL ATTENTION): 1) Precueing experiments (Posner et al., 1978) - person stays fixated on cross in center of image while a valid or invalid cue (arrow pointing toward or away from where box would appear) is given, asked to press key when square appeared, 2) Results: people responded to stimuli FASTER (pressed key quicker when square appeared) when given a valid cue even though they didn't fixate on the cue (looked at the cross)

Memory Color Effect

Effect on perception of prior knowledge of the typical colors of objects - research shows that b/c people know the colors of familiar objects (ex. stop sign, green tree), they judge familiar objects as richer, more saturated colors than unfamiliar objects w/ same color wavelengths

Global Optic Flow

Everything moves at once in response to movement of the observer's eyes or body - if all angles in the environment change at the same time, no motion is perceived --> ex. when Maria scans a scene from left to right, everything around her (walls, windows, etc.) moves to the left of her field of view, same thing happens when walking through a scene

The Gist of a Scene

General description of the type of scene

Optic Array

Gibson's idea: 1) Structure created by surfaces, textures, and contours in the environment, 2) Array of visual info = many related objects at different angles, optic array = structure of these related objects, 3) Motion is perceived when one part of the visual scene moves relative to the rest of the scene, and no motion is perceived when the entire field moves or remains stationary, 4) Not much neurological support for optic array, more for corollary discharge theory

Physical Regularities in the Environment

Helps explain why we perceive gist of scenes so fast - Regularities: regularly occur, we learn basic rules about how stuff works from regularities --> Physical regularities: we have learned from regularly occurring physical properties of an environment - 1) Spaces within objects have homogeneous (same/similar) colors and nearby objects have different colors (ex. distinguish brown roof from blue house), 2) Light-from-above assumption: we interpret objects with light at the BOTTOM as concave (bending inward) and objects with light at the TOP as convex (bulging outward)

Uneven Illumination: Shadows

How do we know when something is a shadow? 1) Nature of the shape - ex. bricks aren't tree-shaped, so tree-shaped shadow on brick wall can be distinguished from brick wall, 2) Presence of a PENUMBRA: Fuzzy edge of a shadow (cup shadow - has fuzzy edge), 3) If image casting shadow is in our visual field: ex. palm tree is in image where shadow is on brick wall

Neural Activity & Object Perception (???)

How the brain reacts to an object while it is being presented determines our ability to identify objects - study: participants saw Harrison Ford, another person, or a texture & had to indicate what they saw very quickly, 1) most Fusiform Face Area (FFA) activation when correctly identifying HF - shows that FFA is responsible not only for actual face stimuli, but for perception of it (even when it isn't there) HOW???, 2) Just looking at trials w/ HF's face, brain activity predicted ability to correctly identify the face, 3) Main point: brain activity reflects our perceptual experience (what we perceive), not our sensory experience (what is actually there)

Implications of Research on Brain Decoding

If this encoding & decoding process works, it should be possible to predict what person is thinking of with brain activation alone --> We could read minds - if this technology could be done from a distance, we could tell what people are thinking without them knowing

Research about Gist

Indicates that the gist of a scene is processed very quickly: Porter (1976) - description was given to participant (ex. girl clapping) and participants had to judge whether the image described was presented among 16 fast pictures (shown for 250milliseconds/ms) --> participants had 100% accuracy at 250ms (could tell if image described was displayed among 16 images) --> more studies showed that 67ms was enough for participants to judge whether image described was presented

Reading the Brain: Line Orientation Decoders

Kamitani & Tong (2005): study with simple grating stimuli - computer can predict that person is thinking of 1 out of 8 line orientations based on brain activation: 1) Orientation ENCODER is calibrated by determining the relationships between voxel pattern and orientation is determined by measuring the response of the brain to a number of orientations, 2) These data are used to create a "DECODER" program that can determine orientation based on voxel activation pattern, 3) Decoder is tested by measuring brain activation as person looks at different orientations - using decoder to predict the orientation the person is perceiving

Load Theory of Attention & Inattentional Blindness

Line study: 1) Line length estimation task (which is longer of crossed lines) - only 10% of people noticed small square near the cross: difficult length estimation task was HIGH-LOAD (used up most of perceptual capacity), so few resources were left to detect small, task-irrelevant stimulus (square), 2) Line color task (which is green, horizontal or vertical line?) - 55% of people noticed square: color task was easy and LOW-LOAD, so more resources available to notice task-irrelevant stimulus (square)

Binocular Rivalry Studies

MONKEY STUDY: 1) Monkeys trained to push correct button when seeing sunburst or butterfly, 2) Both images are presented together, 3) When monkey indicated that it was perceiving the butterfly, the butterfly neuron is firing (& no butterfly neuron when sunburst button pressed) - has nothing to do with what is presented (b/c both are), but is about what is being perceived, HUMAN STUDY: 1) Image of house in red and face in green are overlaid, 2) When house was being perceived, Parahippocampal Place Area (PPA) was activated, and when face was being perceived, the Fusiform Face Area (FFA) was being activated, 3) Main point: brain activation is reflecting the perceptual experience, not just the activation of receptors/bottom-up processing (which stayed constant in this study regardless of what was perceived/which areas fired)

Functions of Motion/Motion Perception #1

Motion is important to help us understand events in the environment: 1) Motion indicates a lot about interactions between objects and people, 2) Helpful for interpretation (demo with dot & 2 triangles moving around box - we can make up a story just looking at motion), 3) Helpful for navigation - OPTIC FLOW: objects moving past us in the opposite direction that we're moving in - helps us navigate and choose what to attend to (person walking in circle study - navigated around & attended to people walking near her), 4) Motion allows us to monitor changes in the world - AKINETOPSIA: blindness to motion (due to brain damage) - most see choppy images b/c cannot perceive motion, this can be very dangerous (ex. crossing street and don't see car until it is right in front of you b/c you didn't see it move, only see flashing images every few seconds, getting away from danger like animals etc. can be difficult)

Functions of Motion/Motion Perception #2

Motion provides information about objects: 1) Motion attracts visual attention to the presence of objects - Attentional capture - we tend to like fast moving things/things that stand out), 6) We use motion to separate objects from the environment and decide what is most important (usually what is moving), motion allows us to segregate ambiguous stimuli to see objects (combine things that move together into one object - common fate)

Reading the Brain: Structural & Semantic Decoders

Naselaris et al. (2009): study with more complex stimuli where computer program could predict the structure and semantics of thought using - 1) Structural decoders = line orientation, detail,& position, 2) Semantic decoders = categories like "tool" and "house")

Intensity

Number of photons of light a source emits/amount of light - how strong the color is

Nontransparent Objects

Objects that light doesn't pass through - most objects are nontransparent

Transparent Objects

Objects that light pass through - more rare than nontransparent, ex. water bottle, plastic bag

Behavioral Evidence of Opponent Process Theory

Obtained around the time of the theory (before physiological evidence could be found): 1) Color afterimages: American flag illusion - staring at one image for a while will result in seeing the opposing colors when screen turns white (black = white, yellow = blue, green = red), 2) Visualizing colors: It's easier to visualize non-opposing color combinations (ex. red & yellow combined = orange) than opposing ones (ex. red & green combined = less certain, maybe brownish or cannot think of color combo), 3) Colorblindness: People are red/green colorblind, or yellow/blue colorblind - cannot see certain pairs of colors, suggesting that these colors are opposing

Physiological Evidence of Opponent Process Theory

Opponent neurons (type of bipolar cell): Excitatory response to light from one part of the spectrum & inhibitory response to light from other part of spectrum - found in RETINA AND LGN (in thalamus): 1) Monkey LGN (in thalamus): SEE DIAGRAM, ex. opponent neurons that like blue & hate yellow (B+Y-) are excited by blue (more likely to fire) and inhibited by yellow (less likely to fire) - compared to spontaneous (typical) firing rate, fire most when hit with blue wavelengths, least with yellow wavelengths, green = in between b/c combo of yellow & blue, red = pretty low b/c not sensitive to red, but more than yellow b/c inhibited by yellow

Coloring Book Theory

Older theory: form is determined and color is used in later stages of processing to fill in form

V4

Part of visual cortex: if there were an area in the brain specifically for processing color in a modular (specific/exclusive way), V4 is most likely to be it

Illusory Motion

Perception of motion that involves perception of stimuli that are not moving

Object Color Perception: Nontransparent Objects

Perception of nontransparent objects color is determined by what wavelengths of light are reflected off of the object: 1) Chromatic colors/hues: have selective reflection - some wavelengths are reflected more than others (based on the matter), resulting in perception of that color (wavelength that is reflected more), 2) Achromatic colors/hues: all light wavelengths are reflected equally across the spectrum (no selective reflection) - resulting in gray/white/black, 3) All wavelengths absorbed = black, all wavelengths reflected (none absorbed) = white

Object Color Perception: Transparent Objects

Perception of transparent object color is determined by what wavelengths are transmitted through the object: 1) Chromatic colors/hues: have selective transmission - only some wavelengths make it through the object/substance (ex. cranberry juice - red wavelength makes it through substance so looks red), 2) Achromatic colors/hues: light is transmitted equally across the spectrum (no selective transmission) - ex. dirty grayish paintbrush water

Overt Attention

Physically moving your eye gaze and attending to objects - vision is clearer in the fovea b/c it's all cones, and smaller & more receptive fields (so more precise), peripheral vision = less clear b/c more rods and larger & less receptive fields --> can be measured w/ EYE TRACKER

Saccadic Movement

Rapid jerky change from one fixation to the next - works with fixation to create coherent visual experience by helping us focus on important stuff (fixation points) perceive scene overall (move between fixations)

What is Responsible for Lightness Constancy?

Ratio Principle: Ratio of an object's reflectance vs. surrounding object reflectance - as long as this ratio stays the same, the perceived lightness will stay the same --> mechanism that does this is unknown, only really works with UNIFORM LIGHTING ACROSS SCENE (uncommon)

Perceived "Color" Depends on Illumination #2

SEE REFLECTANCE CURVE GRAPH: 1) Interaction between wavelengths produced by the illumination (BULBS) and the wavelengths reflected by the green sweater, 2) According to reflectance curve, the sweater reflects mostly medium-wavelength light (expected with green), 3) Actual light reflected from the sweater depends on its reflectance curve and on the illumination that reaches the sweater & is then reflected from it, 4) To determine the wavelengths that are actually reflected from the sweater, MULTIPLY the sweater's reflectance curve at each wavelength, 5) This calculation shows that light reflected from the sweater includes relatively more long-wavelength light when it is illuminated by incandescent/tungsten light (ORANGE line in graph) than light from LED bulb (BLUE line in graph), 6) COLOR CONSTANCY: the fact that we see sweater as green even though the wavelength composition of the reflected light differs under different illuminations = color constancy - without color constancy, sweater color would look diff. in diff illuminations

What directs overt attention? #1

Salience: extent to which stimuli stands out (intensity & difference within environment) - 1) Overt attention is involuntarily directed toward stimuli that is strong/intense or different within the environment - unconscious, immediate attentional process, 2) ATTENTIONAL CAPTURE: involuntary shift of attention due to abrupt, strong stimuli (ex. lightning & fireworks), 3) We attend first to things that stand out in color, orientation, & intensity, 4) Saliency maps: white areas of image = most salient, dark = least salient (see slide - ex. girl in colorful clothes is more salient than background)

Reflectance/Transmission Curve

See slide - white paper = all wavelengths reflected equally, but higher percentage of light reflected, gray card = medium % of light reflected but all wavelengths reflected equally, black paper = low % of wavelength reflected but all wavelengths reflected equally --> Achromatic hues: reflects or transmits all wavelengths equally but at different % of reflectance, Chromatic hues: reflects or transmits different wavelengths more than others, so look colored

Local Disturbance in Optic Array

Selective covering/uncovering pieces of visual display - if change happens in one area of environment and not others, motion is perceived b/c it is different --> ex. when Jeremy walks past Maria's field of vision, portions of the optic array become covered as he walks by and are uncovered as he moves on (moving relative to the environment, covering & uncovering stationary background)

Voxels

Small, cube-shaped volumes in brain about 2-3mm on a side --> pattern of voxels activated depends on the task and the nature of the stimulus being perceived

Relationship Between Perception of Particular Stimuli and the Brain

Studies show that brain activity in higher processing areas of the brain is linked to subjective perception and rather than just bottom-up activation of retina/activation of receptors

What Happens When We Attend: #4 Con'td.

Study #3 - 1) Receptive fields in the middle temporal lobe (MLT) in monkeys shifted depending on what the monkey was attending to, 2) Shows that attention can shift the location of a neuron's receptive field

Evidence of the Memory Color Effect

Study: 1) TASK: observers saw pictures of fruits with normal colors (yellow banana, orange orange, etc.) against gray backgrounds AND also viewed a spot of light against same gray background, 2) When the intensity & wavelength of the spot of light were adjusted so the spot was physically the same as the background, observers thought the spot was the same gray as the background, 3) When intensity and wavelength of the fruits' colors were set as physically the same as the background, observers reported fruits being slightly colored (ex. saw yellowish banana against gray background even tho they were the same wavelength & intensity), 4) CONCLUSION: observer's knowledge of the fruit's characteristic colors actually changed experience/perception of colors (saw colors of fruits when they were actually gray like background) - memory has small but important impact on experience of color (contributes to our ability to accurately perceive the colors of familiar objects under diff. illuminations)

Simultaneous Color Contrast

Surrounding an area with a color changes the appearance of the surrounded area --> Afterimage: staring at green box with white inside for a while makes inside look green and outside look pink when switched to white screen - why green? we don't know, but we know our system is taking into consideration what's going on around something and making appropriate corrections

What directs overt attention? #3

Task Demands: We look at what is relevant to what we are doing - 1) Study found that eye movements precede motor movements by fractions of a second (ex. making peanut butter and jelly - look before acting)

Why do men have higher rates of color deficits?

The most common form of color vision deficiency is encoded on the X sex chromosome (only have one X chromosome, so if that one doesn't have necessary stuff to not have color deficit, they will have color deficit - but females have XX, so other X chromosome could be good if one is ass)

Opponent Neurons in Cortex (??? LGN part)

Types of color receptors in V1 and onward: 1) Single-opponent receptive fields (SEE DIAGRAM): in LGN (THALAMUS, NOT PRIMARY VISUAL CORTEX) - excitatory center-inhibitory surround receptive fields on these receptors, for perception of color in REGIONS, 2) Double-opponent receptive fields (SEE DIAGRAM): for perception of color BOUNDARIES - distinguishes edges b/c in two rectangles

Lightness Constancy Problem

Visual system problem: Intensity relationships (intensity of light reaching the eye from an object) depends on: 1) Illumination: total amount of light that is striking the object's surface, 2) Reflectance: Proportion of light reaching eye that the object reflects into our eyes, 3) when LIGHTNESS CONSTANCY occurs, our perception of lightness depends on reflectance, NOT illumination, 4) Objects that look black reflect <10% of light, objects that look black reflect 10-70% of light, objects that look gray reflect 80-95% of light

Color Constancy

We perceive the colors of an object as being relatively constant even under changing illuminations - our perceptual system adjusts

Lightness Constancy

We perceive whites, grays, and blacks (lightness) as staying about the same shade under changing illuminations

Color-Matching and Screens

We're experiencing color-matching every time we look at a screen - screens are just pixels with combinations of red, green, and blue wavelengths that trick cone receptors into thinking there are many colors there

Hues

What we think of as color: 1) Pure/unique hues (colors): red, yellow, green, & blue, 2) Beyond pure hues/colors - we can discriminate between 200 total different hues

Change Blindness

When one fails to recognize that what they are seeing is different from before b/c of attentional limitations (inability to realize that what was just there is different in the next moment): 1) Less likely to notice changes in less important things (ex. shirt color) than things important to the current task, 2) Study: video shown with changes between shots (scarf there and then gone, plate color changed) - only 1 in 10 people noticed changes, 3) Flicker paradigm: we must fixate on something to notice it's changing - blank flash between images wipes perceptual system/sensory memory, so image just seen is wiped (ex. plane picture changes but blank in between makes it hard to notice b/c can't fixate)

Binocular Rivalry

When presented with different images in each eye, we perceive one & then the other, not both - 1) Eyes don't incorporate the 2 images, but see them separately & perceptual system controls which image is perceived (alternates between them), 2) Each eye is fighting to dominate perception/what is perceived , 3) Testing binocular rivalry is a way to test whether brain activity is more correlated w/ sensory experience (bottom-up processing) or perceptual experience (top-down processing), ANSWER = perceptual experience

Inattentional Blindness

When you fail to see something in plain sight b/c you are engaged in a different task - 1) Study: participants asked to determine which line in the cross was longer, missed the box in the 6th trial b/c paying attention to line length, AND video with gorilla/moonwalking bear, 2) Factors that help us "see" (perceive) what we may have ignored: people with ADHD have less inattentional blindness b/c their attention darts around/they're distracted easily by stimuli and are less likely to focus too hard on one stimuli and miss another - so more likely to see moonwalking bear/gorilla in basketball video experiment , younger people perform better (maybe more curious, or attention span is shorter)