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PSYC 440 > Sensation and Perception - Vision > Flashcards

Sensation and Perception - Vision Flashcards

1
Q

What kind of process is perception?

A

an inductive process

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2
Q

What is invariance in perception?

A

how do we cognize a pencil from different angles and still know it is a pencil

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3
Q

How do features affect perception?

A

How do we extract particular features even though those features are particularly abstract fir the basic units of cognition and perception

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4
Q

What is the relationship between representations and perception?

A

What representations help us recover or recognize an object?

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5
Q

What is domain specificity?

A

the idea that if we are thinking about understanding the brain as a reverse engineering problem we have these computational units with specified input and the kind of input that goes into each part of the system what is the desired input for a certain module of the system

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6
Q

How is the perceptual system built to make inferences?

A

those inferences are based on how neurons are wired and they are not explicit - this is based on innate mechanisms or high level phenomenon that come from the environment

-similar to gestalt psychology - the whole is always different than the sum of its parts

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7
Q

How is perception an inference according to helmholtz?

A

argued that sensory inputs are at least incomplete - the retina is 2d but we perceive the world as 3d

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8
Q

What is the doctrine of specific nerve energies and why is it right for the wrong reasons?

A

helmholtz supported this and he believed that stimulation of visual neurons produces visual sensations and that perception must be adding something to sensation and that inferences based on prior experience - such as phylogenetic or ontogenetic experience

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9
Q

Does the brain have access to light?

A

it does not it has access to receptors at the periphery like photoreceptors which transform light into electrical signals the brain can process

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10
Q

How is light transduced at the retina?

A

photoreceptors in the retina turn light luminance into electrical signals
-this will make the light available to the nervous system in various ways

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11
Q

What do rods process?

A

light and dark contrast

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12
Q

What do cones process?

A

color

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13
Q

When light comes in what happens?

A

it passes through all the nervous tissue and get to the epithelial cells which have photoreceptors hit with photon and they get activated and they are light signals which creates an electrochemical signal to tell us light is there - photoreceptors then send into to a target

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14
Q

What are the outputs of retinal processing or photoreceptors?

A

-they send info to ganglion cells

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15
Q

What do the receptive field of ganglion cells have?

A

center surround organization
-they code for contrast

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16
Q

If there is complete luminance on the entire receptive field of a ganglion cell or none at all what happens?

A

there is no response in either case

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17
Q

How do retinal ganglion cells encode color?

A

they are sensitive to different wavelengths of light like medium versus short and have center surround organization like red in center green in surround and if the entire receptive field is stimulated the color will be gray

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18
Q

Since the world around us is isolumin and the same wavelengths of light what does this mean for our color vision system?

A

it has made some adaptations or inferences to particular wavelenghts of light - light is affected by the light surrounding it

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19
Q

What are the assumptions we make when inferring a surface color from cone responses?

A

-we assume a gray world and the average surface is gray or achromatic
-we assume there is a minimal number of illuminant usually one which is the sun
-we assume that the typical causes for contour and junctions (xjunctions signal transparency or hard shadow)
-we assume the general physics of light than being in shadow does not change a hue and there are inter-reflections (which is how light bounces off surfaces)

-some of these assumptions are built into the way signals are processed in the retinal ganglia - very early in the visual system assumptions are made about what the world looks like are being used to infer what must be out there

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20
Q

What was in the hubel and wiesel experiment?

A

put an electrode into neuron in primary visual cortex or v1 and the pops showed aps and show neural activity - showed slits of light oriented in different ways - Xs are excitatory and triangles are inhibitory
-showed that the neuron is sensitive to location and orientation of bar length and has on and off structure - super wide nothing happens because you stimulate the inhibitory and excitatory parts of the receptive field

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21
Q

How do the receptive field in the LGN compare to the ones in V1?

A

LGN - have on/off center surround cells
V1 - the orientation of the light stimulus matters in addition to the location

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22
Q

How do you get the orientation of the light stimulus to matter in V1?

A

buildup a line of the LGN receptive fields and stack them ontop of each other to get them to be sensitive to an orientation (look at slide 22 for image)
-this means that one v1 neuron is specifically connected to these certain LGN cells and they are oriented to the surface of the eye and the V1 neuron is getting low level information about a particular orientation

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23
Q

How do V1 neurons function as general pattern analyzers (spatial frequency channels)?

A

-you have LGN neurons which focus on orientation which feed into v1 cells which focus on frequency
-these cells are retinotopically specific and respond to light on certain parts of the retina

24
Q

What is low spatial frequency?

A

means as you cover space the alterations between light and dark happen uncommonly or unfrequently so a low frequcency spatial signal is thick

25
Q

What is high spatial frequency?

A

as you cover space the alteratons between light and dark happen commonly so the light is going to be thin bars

26
Q

As you go up the y axis what happens to the iterations of light and dark bars?

A

they turn gray because as you go up the yaxis which is contrast it is decreasung

27
Q

What animals are used in visual experiments?

A

cats and ferrets - not mice but mice are good for olfaction

28
Q

In terms of spatial frequcny what must the stimulus match?

A

the svale of the spatial freuqany for the cell to elicit a strong response cause of on /off center and surround

29
Q

What are hybrid images used to demonstrate?

A

that scene recognition uses distinct spatial uses distinct spatial frequency channels with different time constraints

30
Q

When images are presented rapidly 30ms what frequency information are participants biased towards?

A

low frequency information

31
Q

When images are presented to a participant with more time like 150ms what information predominates?

A

high frequency information

32
Q

As a result of the temporal order of spatial frequncy domination how can we describe scene processing?

A

-we can describe it as from coarse to fine order

33
Q

If you are given enough time to stare at a hybrid image?

A

you can flip between LF and HF

34
Q

What are gabor patches?

A

a mathematical representation of V1 receptive fields

35
Q

How are gabor patches made?

A

-they are amde up by multiplying a sinusoid optimal for specifying scale with a gaussian curve whcih is important for orientation

36
Q

How does a sinusoidal curve specify scale?

A

it shows the sptial freuqncy bases on how often it goes up and down which shows alterations between light and dark

37
Q

How does a gaussian curve specify orientation?

A

the larger the stdev of a gaussian curve the larger the receptive field meaning more possible orientations

38
Q

What does a gabor patch specify for?

A

both spatial frequcny and orientation

39
Q

What other type of detector do V1 neurons function as?

A

edge and contour detectors - visual neurosicentists are inetrested in how do you extract edges and contours

40
Q

What are contours invariant to and what does that mean?

A

-they are invariant to intensity so contours give us information about the reak world and about shapes in the real world so there is a model of object recognition which is based heavily on contour abstraction and edge abstraction

41
Q

How do neurons detect an edge?

A

so if you have a neuron with low spatial frequcny that responds to light on left side and dark on rifht side and it will tell you there us an edge
-there will be a lack of gradation between light telling you there is an edge or contour there

42
Q

How do edges differ from gradients?

A

an edge will respond at any frequecny cause there is a steep drop off, but a gradient will not respond at higher spatial frequencies cause there is no difference between light and dark in that small area which is how we differ edges from gradients

43
Q

How can you detect an edge via a logic gate?

A

can build a logic gate which responds strongly only when you have a stack of gabors in the same orientation and location and vary in spatial frequency and that is going to give you a sharp edge

44
Q

Are visually recognizing things and being able to utilize visual information from motor movements the same thing?

A

no they are not

45
Q

Since the brain is organized in a hierarchical manner how can you build a computer to replicate this in terms of vision? What are some current problems with the current programs designed?

A

retina gets transformed into its electrical signals and this gets passed into center surround cells - then the contours are combined into basic features and these features can be used to identify a set of shapes or specific objects and we can combine these shapes in ways to see 3 dimensional representation of what we are looking at

-however current program just geerate contours and we cannot get the whole image from conoturs - also program is really bad at abstracting visual information from nature

46
Q

Who are the two patients which using double dissociation logic we gained some insight into two gross pathways in the visual system?

A

patient DF - shape agnosia
patient RV - optic ataxia

47
Q

What was going on with patient DF?

A

-has shape agnosia where is being shown an object and cannot tell you what the object is - individual characteristsics of the object are intact but cannot piece together what the object is
-has a difficulty in copying images
-navigating space aka the slot task is quite well spared - given remote which has a gyroscope and recording angle feeding into a computer and df is terrible with matching but they are good at the motor component when they put the remote into the slot (posting)
-can use visual information to plan a motor movement but not to match or draw
-impaired in shape processing

48
Q

Does DF’s behavior provide evidence for independent neural coding of visual recognition and visually guided behavior?

A

no need a patient with the complementary condition - double dissociation

49
Q

What was going on with patient RV?

A

-had optic ataxia
–cannot do the posting task but can do the matching task
-in aperture test DF can change the shape of grip but when going to reach object cannot get it right
-in grasp calibration you pick up an irregularly shaped object do some calculations to figure out the best way to pick it up - rv is veyr impaired at this - rv picks up irregular rocks at corners which unimpaired people know will cause it slip out
-not as impaired as DF in shape processing got 90% right

50
Q

What is a weakness in the case study between RV and DF?

A

-have different deficits but RV got 90% in shape recognition which is a very easy task - this means these two systems are not entirely independent - some of the deficits in tehse tasks are teh results of compensatory abilites

51
Q

What are the two different neural pathways for extracting different sets of invariant properties for different types of tasks?

A

-there is the dorsal where pathway
-there is the ventral what pathway

52
Q

What is the dorsal where pathway include?

A

fluency because it is terminating in the frontal cortex where you have to plan speech and movement and motor planning - rv has deficit here and has injury in parietal cortex

53
Q

What is the ventral what pathway include?

A

comprehsion and wernickes pathway and this is temporal lobe - df has deficit here

54
Q

Using your visual system to guide movement relies on different information or pathways than recognizing objects but what is an issue when thinking about this in the real world?

A

how can you manipulate something if you cannot extract shape information or how can you extract shape information if not to manipulate it

55
Q

How well can we map functional and anatomical models to one another?

A

-on a functional model can point where we think df and rv might have deficits but it is hard to do the same thing on anayomical map we have designed using retrograde and anterograde tracers in monkeys
-df has lesion in lateral occipital complex but that does not mean we can attach his defiict to that area

56
Q

What did broadmann do with fmri mapping and cytoacrhitecture?

A

did fmri mapping to link functions to anatomical regions of the cerebral cortex

57
Q
A

PSYC 440 (13 decks)

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