PSYC 406 - Quiz #2

Gestalt psychology

"The whole is greater than the sum of its parts."

Red-Green Metamers (Concept)

(a) The long-wavelength light that looks red and the shorter-wavelength light that looks green mix to produce the same response as does the medium-wavelength light that looks yellow (b)

Principle of closure (Gestalt Principle)

- All else being equal there is a tendency to see lines continuing in the same direction. - Closed contour is preferred to an open contour. - Principle of closure is stronger than good continuation.

Image Pixels (Concept)

- Each pixel is a small square that shows a single color - An 800 x 600 image is 800 pixels wide by 600 pixels high, 480,000 pixels in all (0.5 megapixels) - Digital cameras today produce images with several megapixels per image, say 8000 x 6000 (about 50 megapixels total!)

Results from a hue cancellation experiment

- We can use the hue cancellation paradigm to determine the wavelengths of unique hues. - Unique hue: Any of four colors that can be described with only a single color term: red, yellow, green, blue. - For instance, unique blue is a blue that has no red or green tint.

Does everyone see colors the same way?—No. (Concept)

1. About 8% of male population and 0.5% of female population has some form of color vision deficiency: "color blindness." 2. Color-anomalous: A term for what is usually called "color blindness." Most "color-blind" individuals can still make discriminations based on wavelength. Those discriminations are just different from the norm.

Summary of the Principle of Middle Vision (Concept)

1. Bring together that which should be brought together 2. Split asunder that which should be split asunder. 3. Use what you know. 4. Avoid accidents 5. Seek consensus and avoid ambiguity.

Colors very rarely appear in isolation. Usually, many colors are present in a scene. When many colors are present, they can influence each other. (Concept)

1. Color contrast: 2. Color assimilation:

Does everyone see colors the same way?—Maybe. (Concept)

1. Cultural relativism: In sensation and perception, the idea that basic perceptual experiences (e.g., color perception) may be determined in part by the cultural environment. 2. Various cultures describe color differently.

Three steps to color perception (Concept)

1. Detection 2. Discrimination 3. Appearance

Does everyone see colors the same way?—Yes. (Concept)

1. General agreement on colors 2. Basic color terms: Single words that describe colors and have meanings that are agreed upon by speakers of a language. 3. In English, these rules yield 11 terms: red, green, blue, yellow, black, white, grey, orange, purple, brown, and pink

Hue cancellation experiments (to test opponent color theory)

1. Start with a color. The goal is to end up with pure blue. 2. Shine some red light to cancel out the green light. 3. Adjust the intensity of the red light until there is no sign of either green or red in the blue patch.

Gestalt figure-ground assignment principles (Concept)

1. Surroundedness 2. size 3. symmetry 4. parallelism 5. extremal edges

Ewald Hering (1834-1918) noticed that some color combinations are "legal" while others are "illegal

1. We can have bluish green (cyan), reddish yellow (orange), or bluish red (purple). 2. We cannot have reddish green or bluish yellow.

Good continuation (Gestalt Principle)

A Gestalt grouping rule stating that two elements will tend to group together if they lie on the same contour.

Middle vision (Concept)

A loosely defined stage of visual processing that comes after basic features have been extracted from the image (low-level vision) - Involves the perception of edges and surfaces - Determines which regions of an image should be grouped together into objects

Perceptual committees (Concept)

A metaphor for how perception works Many different and sometimes competing principles are involved in perception. Perception results from the consensus that emerges.

Additive color mixing:

A mixture of lights If light A and light B are both reflected from a surface to the eye, in the perception of color, the effects of those two lights add together.

Subtractive color mixing:

A mixture of pigments - If pigment A and B mix, some of the light shining on the surface will be subtracted by A and some by B. Only the remainder contributes to the perception of color

Gestalt grouping rules (Concept)

A set of rules that describe when elements in an image will appear to group together. 1. Good continuation, 2. principle of closure, 3. Texture segmentation, 4. Similarity, 5. Proximity, 6. Parallelism, 7. Symmetry

Symmetry (figure-ground principle)

A symmetrical region tends to be seen as figure.

Ambiguous figure (Concept)

A visual stimulus that gives rise to two or more interpretations of its identity or structure based on the rules.

Agnosia vs Prosopagnosia (Concept)

Agnosia: Failure to recognize objects in spite of the ability to see them. Prosopagnosia: An inability to recognize faces.

Committee rules (Concept)

Always follow the laws of physics and avoid accidents Accidental viewpoint: A viewing position that produces regularity in the visual image that is not present in the world.

Achromatopsia:

An inability to perceive colors is caused by damage to the central nervous system.

Step 2: Color Discrimination The principle of univariance:

An infinite set of different wavelength-intensity combinations can elicit exactly the same response from a single type of photoreceptor.

Camouflage

Animals exploit Gestalt grouping principles to group into their surroundings.

Computer/Digital Pixels (Concept)

Any color can be represented by combination of red/green/blue light Any color can be represented by three numbers

Texture segmentation (Gestalt Principle)

Carving an image into regions of common texture properties.

Color assimilation

Color assimilation: A color perception effect in which two colors bleed into each other, each taking on some of the chromatic quality of the other.

Color contrast

Color contrast: A color perception effect in which the color of one region induces the opponent color in a neighboring region.

Basic Principles of Color Perception (Concept)

Color is not a physical property but a psychophysical property. "There is no red in a 700 nm light, just as there is no pain in the hooves of a kicking horse." -Steven Shevell (2003)

Step 3: Color Appearance (Concept) Color space:

Color space: A three-dimensional space that describes all colors.

Several types of color-blind/color-anamolous people (Concept)

Deuteranope: Due to absence of M-cones. Protanope: Due to absence of L-cones. Tritanope: Due to the absence of S-cones. Cone monochromat: Has only one cone type; truly color-blind.

Metamers:

Different mixtures of wavelengths that look identical; more generally, any pair of stimuli that are perceived as identical in spite of physical differences.

Objects in the brain

Extrastriate cortex: Brain regions bordering primary visual cortex that contains other areas involved in visual processing. V2, V3, V4, etc.

Prosopagnosia

Faces: An illustrative special case Face recognition seems to be special and different from object recognition. Prosopagnosia: An inability to recognize faces. https://www.youtube.com/watch?v=vwCrxomPbtY

Figure-ground assignment (Concept)

Figure-ground assignment: The process of determining that some regions of an image belong to a foreground object (figure) and other regions are part of the background (ground). - figure refers to "the main object that is recognized in an image"

Animals provide insight into color perception in humans (Concept)

Food It is easier to find berries and determine when they are ripe with color vision. Reproduction Colorful patterns on tropical fish and toucans provide sexual signals. mandrills—face color is often an advertisements to potential mates

But!! Just because cultures describe color differently does it mean they experience colors differently?! - No

Heider Rosch investigated Dani (Highlands of New Guinea). They found that the Dani's two colour categories mola and mili were better labelled 'white-warm' and 'dark-cool' than simply WHITE and BLACK.

Step 3: Color Appearance --> HSB color space:

Hue: The chromatic (color) aspect of light. Saturation: The chromatic strength of a hue. Brightness: The distance from black in color space.

Extremal edges (figure-ground principle)

If edges of an object are shaded such that they seem to recede in the distance, they tend to be seen as figure.

Gestalt

In German, "form" or "whole."

Experiment to determine differences in color perception (Concept)

It is easier to remember which of two colors you have seen if the choices are categorically different.

Proximity (Gestalt Principle)

Items that are near each other tend to group.

Cone-opponent cells in the LGN

L-M or L+/M- cell is excited by redder hues in its center and inhibited by greener hues in its surround. These are single-opponent cells

11 basic terms in English are similar to many other groups'.

Languages with 11 basic color terms: Arabic (Lebanese), Bulgarian, English, German, Hebrew, Japanese, Korean, Spanish, Zuni, ... Hungarian (12), Russian (12), Dani (2), Berinmo (5)

Step 2: Color Discrimination (Concept) What happens if only one photoreceptor is at work?

Lights of 450 and 625 nm of the same intensity, each elicit the same response from the photoreceptor

Afterimages: A visual image seen after a stimulus has been removed.

Negative afterimage: An afterimage whose polarity is the opposite of the original stimulus. Color specific adaptation Colors are complementary. Red produces green afterimages and blue produces yellow afterimages (and vice versa). This is a way to see opponent color theory in action.

Object Discrimination vs Landmark discrimination (Concept)

Object discrimination- a monkey was shown one object such as a rectangular solid and was then presented with a two-choice tasks. if the monkey pushed aside the target they were rewarded with food under the object. - part of the temporal lobe was removed in some monkeys. after behavioral testing showed that the object discrimination problem was very difficult for monkeys with their temporal lobes removed. indicates that the pathway that reaches the temporal loves is responsible for determining the identity of an object. Landmark Discrimination - the monkey's task was to remove the cover of the food well that was closest to the tall cylinder. - other monkeys have their parietal lobes removed and they had difficulty solving the landmark discrimination problem. indicates that the pathway that leads to the parietal lobe is responsible for determining the location of an object.

Opponent color theory (Concept)

Opponent color theory: The theory that perception of color depends on the output of three mechanisms, each of them based on an opponency between two colors: red-green, blue-yellow, and black-white.

Parallelism (Gestalt Principle)

Parallel contours are likely to belong to the same group.

Inferotemporal (IT) cortex

Part of the cerebral cortex in the lower portion of the temporal lobe, important for object recognition. - What pathway

Qualia:

Private conscious experiences of sensation and perception. - The question, "Is my perception of blue the same as your perception of blue?" is a question about qualia. - An interesting question, then, is "Does everyone see colors the same way?"

Step 3: Color Appearance --> RGB color space

RGB color space: Defined by the outputs of long, medium, and short wavelength lights (i.e., red, green, and blue).

Parallelism (figure-ground principle)

Regions with parallel contours tend to be seen as figure.

How do we recognize objects? (Concept)

Retinal ganglion cells and LGN = Spots Primary visual cortex = Bars

Step 1: Color Detection Three types of cone photoreceptors

S-cones detect short wavelengths. M-cones detect medium wavelengths. L-cones detect long wavelengths.

Landmark discrimination

Select food well closer to the TOWER

Step 1: Detection In the Retinia

Sending signal from S,M,L cones to the brain. Simple signals is not as useful. 1. For example, L- and M-cones have very similar sensitivities, so most of the time they are in close agreement. Computing differences between cone responses turns out to be a much more useful way to transmit information to the brain. 2. Difference between L and M responses contains considerable information about color. Because L and M are so similar, L-S and M-S would be very similar, thus a single comparison between S and (L+M) can capture almost the same information that would be found in L-S or M-S. 3. Thus, the three cone signals are converted into four new signals - (L-M), ([L+M]-S), (S-[L+M]) and (L+M).

Additive color mixing (Concept)

Shining a light that looks blue and a light that looks yellow on an area of paper, the wavelengths add, producing an additive color mixture

Similarity (Gestalt Principle)

Similar looking items tend to group.

The three steps of color perception, revisited (Concept)

Step 1: Detection—S, M, and L cones detect light. - In the retina Step 2: Discrimination—cone-opponent mechanisms discriminate wavelengths. In the Lateral Geniculate Nucleus (LGN) [L - M] and [M - L] compute red vs. green. [L + M] - S and S - [L + M] compute blue vs. yellow. Cone-opponent cells compute the differences in the activities of the three cone types. Step 3: Appearance—further recombination of the signals creates final color-opponent appearance. In the Striate Cortex Double-opponent color cells.

Object Discrimination

Study the object Select the familiar object

Symmetry (Gestalt Principle)

Symmetrical regions are more likely to be seen as a group.

Relatability (Dealing with occlusion) - (Concept)

The degree to which two line segments appear to be part of the same contour. - helps us understand when edges are and are not perceived as the whole object behind occulunders.

Rods obey the principle of univariance and cannot sense differences in color. (Concept)

The moonlit world appears devoid of color because we have only one type of rod photoreceptor transducing light under these scotopic conditions - All rods contain the same photopigment molecule: rhodopsin. - Under dim light conditions, only rods are active, and that is why the world seems drained of color.

Global superiority effect (Parts and wholes) - (Concept)

The properties of the whole object take precedence over the properties of parts of the object.

Size (figure-ground principle)

The smaller region is likely to be figure.

Surroundedness (figure-ground principle)

The surrounding region is likely to be ground.

Trichromacy or trichromatic theory of color vision

The theory that the color of any light is defined in our visual system by the relationships of three numbers, the outputs of three receptor types now known to be the three cones.

Trichromacy or trichromatic theory of color vision: (Concept)

The two wavelengths that produce the same response from one type of cone (M) produce different patterns of responses across the three types of cones

Subtractive color mixing (Concept)

The two-color negate each other. Absorbs most visible light, but allows other colors.

In the primary visual cortex, double-opponent color cells are found for the first time.

These are more complicated, combining the properties of two color opponent cells from LGN.

Most of the light we see is reflected.

Typical light sources: Sun, light bulb, fire We see only part of the electromagnetic spectrum, between 400 and 700 nm. Blue = Short Wavelength Red = Long Wavelength

With three cone types, we can tell the difference between lights of different wavelengths.

Under bright light conditions, the S-, M-, and L-cones are all active.

What receptive field properties of IT neurons are like? (Concept)

Very large—some cover half the visual field Don't respond well to spots or lines Do respond well to stimuli such as hands, faces, or objects

Agnosia

When the IT cortex is lesioned, it leads to agnosias. Agnosia: Failure to recognize objects in spite of the ability to see them. https://www.youtube.com/watch?v=ze8VVtBgK7A

Cells in the inferotemporal cortex of macaque monkeys are... (Concept)

interested in very specific stimuli

"Where" pathway (Concept)

is concerned with the locations and shapes of objects but not their names or functions.

"What" pathway (Concept)

is concerned with the names and functions of objects regardless of location.

PPA (parahippocampal place area)

responds preferentially to places, such as pictures of houses. - Some areas of human cortex are specialized to process certain types of stimuli.

FFA (fusiform face area)

responds to faces more than other objects. - Some areas of human cortex are specialized to process certain types of stimuli.

EBA (extrastriate body area)

specifically involved in the perception of body parts