Chapter 12: Visually Identifying Objects

Question 1

2 Circuits of the visual pathway

Answer 1

1) dorsal pathway: primary visual cortex projects to premotor and MOTOR cortices. Uses spatial info to guide head eye and hand movements. Damage results in inability to physically rotate and object based on visual cues (grabs object at awkward angle)
2) ventral pathway: primary visual cortex projects to TEMPORAL cortices. Stimulus IDENTIFICATION.

Question 2

visual agnosia arises because of ____ pathway damage

Answer 2

ventral. ventral pathway damage results in decreases in shape perception and mental rotation.

Question 3

Sparse coding

Answer 3

compression of sensory information by ignoring spatially and temporally invariant information

Question 4

Efficient sensory coding

Answer 4

tend to encode features that occur most frequently in natural stimuli

Question 5

Grandmother cell coding scheme.

Answer 5

a SINGLEneuron represents an object that receives input from a bunch of feature sensing lower level neurons. ALL lower level neurons must respond SIMULTANEOUSLY in order for the single upper level neuron to fire.

Question 6

Population coding

Answer 6

instead of a single neuron representing an object (like grandmother coding) a specific combination of neurons collectively represent an object.

Question 7

General visual system pathway

Answer 7

photoreceptors —> retina –> LGN —> Striate Cortex V1 (thalamus) —> Extrastriate cortex (dorsal and ventral pathway)

Question 8

retinal on and off center cells receive input from ____ cells

Answer 8

bipolar cells.

Question 9

retinal on-center cells receive input from ___ bipolar cells.

Answer 9

ON bipolar cells. retinal on-center cells repond when a light is turned ON suddenly

Question 10

retinal off-center cells receive input from ___ bipolar cells

Answer 10

OFF bipolar cells. respond when a light is turned OFF suddenly.

Question 11

A cell with a center-surround receptive field will:

Answer 11

respond to stimuli in the centre of their receptive field but can be inhibited by a second stimulus thats applied simultaneously at a nearby location.

Question 12

retinal spatial receptive fields are divisible into an ___ center where robust repsonses occur if stimulated, and an ___ surround.

Answer 12

retinal spatial receptive fields are divisible into an EXCITATORY center where robust repsonses occur if stimulated, and an INHIBITORY surround.

Question 13

how is the inhibitory surround of a retinal ganglion cell created?

Answer 13

due to HORIZONTAL CELLS in the retina. Strongly excited photoreceptors in one retinal location tend to inhibit their less excited neighbours.

Question 14

LGN of the thalamus receives ____ input

Answer 14

retinal input from the On or Off center retinal ganglion

Question 15

how many layers of LGN. What are they?

Answer 15

6 layers.

4 THICK layers = parvocellular. receies input from small retinal ganglion cells, and conveys color and luminance information.

2 THIN layers = magnocellular large neurons. Receives input rom large retinal ganglion cells. Color insensitive.

Question 16

individual LGN neurons receive ____ input from retinal ganglion cells of the SAME TYPE. Explain

Answer 16

individual LGN neurons receive CONVERGING input from retinal ganglion cells of the SAME TYPE.

On center retinal cells synapse onto LGN receptive fields that correlate to on-center LGN nuclei.

Question 17

multiple LGN neurons converge onto 1 _____ ___ ___

Answer 17

V1 simple cell (of the same type.)

Question 18

most V1 neurons respond far better to ___ and __- rather than beams of light

Answer 18

lines and edges

Question 19

__ ___ of the V1 respond to lines of a particular orientation and location. Explain why V1 simple cells are more sensitive to lines rather than spots?

Answer 19

SIMPLE CELLS of the V1 respond to lines. They are more sensitive because each simple cell receives CONVERGING input from MULTIPLE LGN neurons whose receptive fields are all the SAME TYPE (all on-center/ off-center), and ARRANGED IN A LINE.

If LGN cells that are all ON-center converge onto a specific V1 simple cell, that V1 will respond when light falls across the on-centers.

Question 20

a V1 simple cell fires only when:

Answer 20

all of its input neurons (LGN and thus retinal cells) are active simulatenously (grandmother coding)

Question 21

V1 Complex cells receive ____ input from multiple ___ ___. What does this allow them to do?

Answer 21

Compex cells receive converging input from multiple V1 SIMPLE CELLS. complex cells respond to line-shaped stimuli at multiple locations that correspond to different V1 simple cells of that specific sensory visual field.

Question 22

the Orientation of a preferred stimulus ____ through successive neurons in a ___ ___ pattern.

Answer 22

the Orientation of a preferred stimulus ROTATES through successive neurons in a PIN WHEEL pattern.

V1 thalamic region thus has neurons capable of responding to lines and edges of all possible orientations.

Question 23

T/F: V1 neurons fire when looking at the interior of an object

Answer 23

false. V1 neurons function like edge detectors in imaging processing. allows you to see the most important info needed to see the genuine object.

Question 24

How is motion identified?

Answer 24

V1 neurons have a very small and specific receptive field and thus it is hard to detect the true motion of an object.

Middle Temporal Area between the occipital and temporal lobe receives input from many V1 neurons to look at dif edges of a moving object and the V1 neurons firing to reveal the true direction of movement.

the MTA thus combines info from multiple V1 neurons whose receptive fields are aimed at dif segments of the moving contour.

Question 25

where are opponent cells? What are they sensitive to?

Answer 25

in the retina. they are sensitive to luminance contrasts (dark red spot on light red background)

Question 26

Which type of cells in the V1 thalamic layer are responsible for detecting color contrast? how do they do this?

Answer 26

Double opponent V1 cells are responsible for color contrast. They exhibit one type of cone opponency in their receptive field CENTER, and another type of cone opponency in their receptive field SURROUND

ex/ in the center, they have L-cone activation (and M-inactivation), but M type activation and L cone inactivation in the surround. This allows them to detect red light in the center and green light in the surround.

Question 27

T/F V1 double opponent cells have larger receptive fields than V1 simple cells (orientation cells)

Answer 27

true. They have less orientation selectivity.

Question 28

What are glob cells? where are they located?

Answer 28

glob cells are color-sensitive cells that have HUE CONSTANCY (allow us to maintain color perception in all amounts of light) that are located in the extrastriate area (visual cortex)

Question 29

face selective neurons are located in the

Answer 29

temporal love. they don’t fire if the face is scrambled or if the eyes are missing. Each face is encoded by a combination of simulatenously activated neurons.

Question 30

Which area of the human brain contains the most face selective neurons? When is this area also activated?

Answer 30

the fusiform face area in the temporal lobe. Also activated in response to other complex visual objects.

Question 31

What are category sensitive neurons? Where are they located?

Answer 31

they behave as if they recognize a category boundary between dogs and cats. or objects. Found in the PFC and the temporal cortex.