Visual Perception cog 305

In order to summarize the Gestalt psychologists' movement in a few words, one might say

"The perceptual whole is different than the sum of its parts."

Pictorial Cues

- a monocular cue - create an impression of depth on a flat surface Interposition Cue-the blocking of your view of one object by some other object Linear Perspective - distant objects produce a smaller retinal image - the pattern in which parallel lines seem to converge as they get farther and farther from the viewer

Lateral inhibition

- a pattern in which cells, when stimulated, inhibit the activity of neighboring cells. -

Binocular disparity

- can induce the perception of depth even when norther distance cues are present

Hubel and Wiesel

- documented the existence specialized neurons within the brain, each which has a different type of receptive field and diff kind of visual trigger

Cones

- less sensitive than rods and need more incoming light to operate at all. - sensitive to color differences. - three types of cones each having its own pattern of sensitivities to different wavelengths - they enable you to discern fine detail (acuity)

Organization and Features

- neither goes first - parallel processing; different brain areas doing their work at the same time.

Photoreceptors

- specialized neural cells that respond to light - two types; rods and cones

Helmholtz

- there is simple inverse relationship between distance and retinal image size -If an object doubles its distance from the viewer, the size of its images is reduced by half, etc. -believed that we were calculating unconsciously called it unconscious inference

Perceptual constancy

- we perceive the constant properties of objects in the world even though the sensory info we receive about these attributes changes whenever our viewing circumstances change Example - size constancy; correctly perceiving the sizes of objects in the world despite the changes in retinal-image size created by changes in viewing distances shape constancy, brightness constancy

Gestalt

- your perception is guided by principles of proximity and similarity

Distance Cues

-features of the stimulus that indicate an objects's position. -eyes look out from slightly different positions; each eye has a different view - difference between two eyes is binocular disparity - motion parallax - the projected images of nearby objects move more than those of distant ones

Center surround cells

-light presented to the central region of the receptive field has one influence while light presented to the surrounding ring has the opposite influence. -If both the center and surround are strongly stimulated the cell will fire neither more nor less than usual - the further the edge is from th cell's preferred orientation, the weaker the firing will be, and edges sharply different from the cell's preferred orientation will elicit virtually no response

Monocular distance cues

-perceive depth with one eye closed -adjustment the eye makes to see the world clearly. the amount of adjustment depend on how far away the object is.

single-cell recording

-procedure through which investigators can record, moment by moment, the pattern of electrical changes with a single neuron. - interested in is the cells firing rate, measured by spike per second - can figure out what job the neuron does within the broad context of the entire nervous system - allows us to define the cell's receptive field; the size and shape of the area in the visual world to which that cell responds

Rods

-sensitive to low levels of light - colorblind; can only distinguish different intensities if light but no hue

If a cat casts a 5 millimeter image on your retina when it is 10 feet away from you, that same cat will cast an image that is ________ millimeters when it is 20 feet away from you.

2.5

Neural Synchrony

If neurons detecting a vertical line are firing in synchrony with those signaling movement, then these attributes are registered as belonging to the same object. If they are not in synchrony, the features are not bound.

Which of the following would NOT be considered an advantage of parallel processing in the visual system?

Information is processed only once, making it efficient.

Molly went to the mall and parked her red car under a tree. When she returned to her car a few hours later, only half of the car was still in the shade. How will Molly perceive this situation?

Molly will perceive the car as a single color, despite the changes in lighting.

Which of the following statements about the visual stimulus, light, is FALSE?

Red light is associated with longer waves, relative to blue light.

Which of the following statements most accurately describes visual illusions?

The cognitive architecture that helps us in most cases causes illusions in other cases.

Describe the process by which visual information is processed in the brain.

The process by which visual information is processed in the brain starts with light, which passes through the lens and the cornea. Once the retina's photoreceptors absorb the light, it is split off into rods and cones which convert light into neural energy. Then the photoreceptors are sent through the second layer of interneurons to the ganglion cell layer of the retina. Information gathered throughout these layers is then projected within the optic nerve to the lateral geniculate nucleus (LGN), which is the main pathway to the primary visual cortex. Axons from the retina are transferred to several areas of the brain to control circadian rhythm and coordinate eye movements.

Some people have sustained brain damage and lost the ability to identify color. Other people sustained damage to a different area of the brain and lost the ability to detect motion. What does this indicate about our visual system?

We have specialized areas for processing different kinds of visual information.

It seems inefficient to need to rely on so many different cues for depth perception. Why, then, do we have so many disparate cues?

We use different cues in different situations.

The moon often looks very large when it is low in the sky, but looks smaller when it is high in the sky. Which of the following could account for this phenomenon?

When the moon is lower in the sky, other objects like buildings or trees provide a reference point for size comparisons.

Which of the following does NOT provide an example for parallel processing in the visual system?

You have two eyes that process different information, but work at the same time.

One way that we can perceive depth is through our awareness of the adjustment our lens is making. This cue would be

a monocular depth cue

The lateral geniculate nucleus (LGN) acts as

a way station between the eye and the occipital cortex, located in the thalamus.

What system

activation from the occipital lobe is passed along to the cortex of the temporal lobe - lesions here show visual agnosia - inability to recognize visually presented objects; show little disorder in recognizing visual orientation or in reaching

Brad is able to read a clock, but is unable to see the arms of a clock move from position to position. He is suffering from

akinetopsia

A researcher wishes to define the receptive field for a particular neuron in the visual cortex. To do this, the researcher will need to specify

an area within the visual field wherein the cell will fire if the target appears.

The cues to depth perception:

are based on principles of physics

Human brains have a distinct division-of-labor strategy. Each task is achieved as a result of multiple brain areas working together. But the work of the various parts of the brain must be compiled into a finished whole. The issue of how this reassembly works is referred to as the

binding problem

Fovea

center of the eye - the cells in fovea are distinctive; better at discerning visual detail

Despite the fact that sensory stimuli can change from moment to moment, we perceive the details (color, shape, etc.) of an image to be stable because of

constancy

A researcher has identified the receptive field for a neuron and has determined that the receptive field has a center-surround organization. If the researcher were to shine light into the entire receptive field, including both the center and the surrounding areas, we would expect the neuron to

continue firing at its resting rate

Conjunction Errors

correctly detecting the features present in a visual display, but making mistakes about how the features are bound together.

You are at the zoo watching a tiger sleep. It suddenly awakes and lurches in your direction. Spatial position would NOT provide information about the tiger's

dangerous nature

Cells detecting th boundary of a surface are subject to less lateral inhibition that cells detecting the center of the same surface. This leads to an effect called

edge enhancement

Julie has sustained damage to the "what" system in her brain. She will likely have difficulty with which of the following tasks?

identifying a chair

Shadowing can provide a cue for depth. For example, if a shadow appears on the bottom of a circle, the object appears convex. However, if the shadow appears on the top of the object, it appears concave. This happens because

in the real world, light comes from above more often than from below.

The blockage of one's view by another object can provide information about depth perception. This is termed

interposition

Cells A and B receive the same high levels of stimulation, but Cell A shows a lower level of activity relative to Cell B. A likely explanation for this fact is that Cell A

is being laterally inhibited by other nearby cells.

Parvo cells are similar to magno cells in what way?

location in the visual system

Because of its center-surround organization, a neuron that has its entire receptive field exposed to bright light will

maintain the same rate of firing as if there was no light presented.

Krista is sitting on a bench, watching the world go by. She notices the people who are near to her move across her retina more quickly than the cars in the distance move. This effect is called

motion parallax

As you move toward an object, the object gets larger on your retina. This is called

optic flow

Single-cell recordings measure the ________ of individual neurons.

pattern of firing

M Cells

provide the input for the LGN's magnocellular cells and are specialized for the detection of motion and the perception of depth.

P Cells

provide the main input for the LGN's parvocellular cells and appear to be specialized for spatial analysis and the detailed analysis of form

Someone with akinetopsia would have difficulty with all of the following EXCEPT

recognizing faces

The importance of vision for humans is reflected in the

relative size of the visual cortex.

The ________ is the part of the eye involved in transducing light energy into neural energy.

retina

Info to the brain

rods and cones report to bipolar cells which excite ganglion cells. Ganglion cells are spread across retina and their axons form a bundle called optic nerve which leaves the eyeball and carries info to various sites in the brain. -first to the lateral geniculate nucleus in the thalamus then it is transmitted to primary projection area for vision in the occipital lobe.

Where system

second pathway, leading to the parietal cortex. guides your action, based on your perception of where an object is located - lesions here have difficulty reaching but problem in identification

Which of the following is NOT considered a monocular cue for depth perception?

similarity

A researcher wishes to determine exactly when a particular neuron is firing. A technique well suited to this purpose is

single-cell recording

Parallel processing

system in which many different steps are going on simultaneously; opposite is serial processing- one at a time - advantage is speed and mutual influence Amon multiple systems

Visual agnosia is associated with damage to which of the following?

the "what" system, which carries information from the occipital cortex to the temporal cortex

Which of the following would NOT be considered part of the fovea?

the area of the retina found far out in the periphery

Lateral inhibition leads to which perceptual experience?

the edge of an object is enhanced.

Which of the following statements about the retina is FALSE?

the photoreceptors communicate directly with the ganglion cells.

Area V1

the site on the occipital lobe where axons from the LGN first reach the cortex -provides a detector for every possible stimulus

Binding Problem

the task of reuniting the various elements of a scene, elements that are initially addressed by different systems in different parts of the brain.

The specialization evident in visual processing shows that

the visual system relies on parallel processing.