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PYB204 > 5&6. Vision and pattern recognition > Flashcards

5&6. Vision and pattern recognition Flashcards

1
Q

what is perception?

A

Awareness of the elements of environment
through physical sensation (Merriam-Webster)

Perception is not just receiving information
through sensation; it involves interpretation
and recognition of the information

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2
Q

What are the types of perception?

A
  • Visual
  • Auditory
  • Tactile (haptic)
  • Olfactory
  • Gustatory
  • Object
  • Space
  • Time
  • Speech
  • Motion
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3
Q

what is required for an object to be visible?

A

For an object to be visible it must either emit or

reflect light

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4
Q

what is light?

A

One way of understanding light is that it is a wave of electromagnetic radiation
– It is a wave, so one dimension of light is its
wavelength

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5
Q

what is the human eye capable of in regards to light?

A

The human eye is only capable of detecting light
within a narrow range of wavelengths
– Within this range of visible wavelengths, different wavelengths give rise to the perception of different
colors

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6
Q

Within the human’s range of visible wavelengths, what do different wave lengths cause?

A

Within this range of visible wavelengths, different wavelengths give rise to the perception of different colors

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7
Q

How does light vary?

A

Light also varies in intensity, leading to the

percept of brightness

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8
Q

what do ciliary muscles do?

A

The ciliary muscles control
the shape of the lens to
accomodate near or far
targets

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9
Q

what happens when the lense is round?

A

Far Blurred

Near in Focus

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10
Q

what happens when the lense is flat?

A

Far in Focus

Near Blurred

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11
Q

what is the retina?

A

A thin, light sensitive membrane located at the back of the eye

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12
Q

what sensory receptors does the retina contain?

A

Contains two types of visual sensory receptors (cells

that convert physical input—i.e., light—into electrochemical signals): rods and cones

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13
Q

what are the rods and cones connected to?

A

other cells

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14
Q

what is the fovea?

A

a small area in the center of the retina, composed entirely of cones
• Where visual information is most
sharply focused

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15
Q

What is the optic disk?

A

the area of the retina without rods or cones

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16
Q

what do rods look like??

A

– long, thin, and blunt

– primarily for peripheral and night vision

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17
Q

what are rods highly sensitive to?

A

– highly sensitive to light, but not to color

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18
Q

what are the rods used primarily for?

A

– primarily for peripheral and night vision

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19
Q

what do cones look like?

A

short, thick, and pointed

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20
Q

what do cones do?

A

detect color

for color vision and visual acuity

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21
Q

what do rods and cones do?

A

Rods and cones convert light energy into
electrical energy via a photopigments (chemicals
that absorb light)

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22
Q

what are photopigments responsive to?

A

Different kinds of photopigments are responsive
to different wavelengths of light
– That is, different kinds of photopigments “see”
different colors

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23
Q

why cant rods provide colour information?

A

There is just one kind of photopigments in rods
(called rhodopsin)—that’s why signals from rods don’t
provide color information

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24
Q

what are the photopigments in cones?

A

Photopigments in cones (called iodopsin) come in

three variations

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25
Q

what do variations in the photopigments in cones sensitive to?

A

Each variation is sensitive to a different range of
wavelengths
– Thus, each variation is tuned to a different range of
colors

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26
Q

how do rods and cones have different levels of acuity?

A

More rods than cones synapse with each ganglion

cell

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27
Q

what are the two major pathways from the retina to the brain?

A

– retina –> lateral geniculate nucleus (LGN) –> V1
(primary visual cortex in the occipital lobe)

– retina –> superior colliculus (SC) (and pulvinar
nucleus)

28
Q

what function does the LGN-V1 pathway serve?

A

conscious aspects of vision (e.g., object recognition)

29
Q

what function does the SC pathway serve?

A

unconscious visual functions (e.g., object localization)

30
Q

What is blindsight?

A

some people with damage to the LGN-V1 pathway can still react to visual stimuli (e.g. point tonthem) although they claim that they cannot see them!

31
Q

what do neurons in the V1 respond to?

A

Neurons in V1 respond to bars of a particular

orientation

32
Q

what does V1 stand for?

A

the primary visual cortex

33
Q

what areas are involved in visual imformation processing beyond the v1?

A

There are multiple visual
areas in the cortex. Each area performs different
types of computation

34
Q

what processing occurs in areas of the cortex that appear later in the information processing stream?

A

in areas that appear later in the information processing stream, neurons respond to more complex patterns

35
Q

what is our visual perception more closely related to?

A

Our visual perception is more closely related to neural activity in the higher visual areas

36
Q

what is the receptive field?

A

Area of the visual field to which a visual neuron responds
It is very small in the beginning, but becomes
increasingly larger in later stages of visual
information processing

37
Q

What is visual information processing?

A

The visual world is broken down into small elements,

and then it is reconstructed

38
Q

What do ganglion cells do?

A

Ganglion cells receive input from multiple receptors that are adjacent to each other

39
Q

what do the two ganglion cells in the retina do to frorm a retinotopic map?

A

Two ganglion cells that are next to each other in
the retina will have receptive fields that are also
next to each other
– Forming a retinotopic map

40
Q

What are the properties of neurons in the LGN?

A

Neurons in the LGN have similar properties
– Center-surround antagonism
– Retinotopic map (i.e., adjacent LGN neurons have
receptive fields on the retina)

41
Q

How do cells and neurons respond in the LGN ?

A

ganglion cells and visual neurons in the
LGN respond simply to the presence of a spot of
light on the retina

42
Q

What are the characteristics and positioning of neurons in the V1?

A

– Receptive fields of two adjacent V1 neurons are still
adjacent to each other on the retina
– These neurons receive input from multiple LGN
neurons
• This enables V1 neurons to function as bar detectors

43
Q

What happens to visual neurons in higher order areas and what does this enable?

A

In higher order areas, neurons have larger
receptive fields by combining input from
multiple lowerlevel neurons
This enables those higherlevel neurons to respond to more complex visual patterns

44
Q

What is agnosia?

A

Impairment of object recognition ability

45
Q

What processes are intact in agnosia patients and what does this cause?

A

In agnosia, processes such as color, shape, and motion perception are intact. This recognizing a whole object is more than just recognizing its parts

46
Q

What are the two cortical pathways for vision?

A

Ventral pathway

Dorsal pathway

47
Q

What is the ventral pathway, what information does it process and what is it important for?

A

– Occipital à temporal
– Processes information about object appearance and
identity
– Important for object perception

48
Q

What is the dorsal pathway, what information does it process and what is it important for?

A

– Occipital à parietal
– Processes spatial information about objects
– Important for guiding action

49
Q

Who was patient DF?

A

– Severe agnosia

– Her visual acuity and nonvisual object recognition are intact

50
Q

What is optic ataxia and what is it associated with?

A

– Intact object recognition
– Inability to use visual information to guide action
– Associated with lesions in the dorsal pathway
(typically in the parietal cortex)

51
Q

What does face perception require?

A

Face perception requires holistic processing

52
Q

What was the study on Larry with regard to face perception?

A

study phase
– Larry had round eyes, a pointed nose, and a
narrow mouth.
– Larry lived in a house with a three-paneled door,
shuttered living room window, and rounded
bedroom windows.

Test phase

  • picture of nose (part condition) and whole face (whole condition)*
  • picture of larry’s door (part condition) and whole house (whole condition)*

Results:
Face condition
- 65% correctly identified faces in isolated condition
- 75% correct in whole condition

House condition

  • 82% in islated condition
  • 80% in whole condition
53
Q

What is involved in the gestalt principles?

A
  • Similarity
  • Closure
  • Good continuation
  • Proximity
54
Q

Wat do we tend to do in relation to template-matching and feature analusis?

A

We tend to recognize different stimuli as the
same object (e.g., letter “A”) irrespective of superficial variation
Gestalt principles don’t really help explain why
Another theory of pattern recognition, template
matching, doesn’t explain this either

55
Q

In the template-matching model what is good matching?

A

Good matching
(successful perception)

Slight difference between input and template (unsuccessful perception)

56
Q

How are visual patterns perceived and what model helps to explain this?

A 
A visual pattern is
perceived as a
combination of
elemental features
– Selfridge’s
pandemonium model
57
Q

What would happen when this pattern is presented on the retina without eye movements?
(HB on top of eachother)

A 
Whole features (e.g., an entire vertical bar) tend
to disappear simultaneously
58
Q

What does the recognition by component theory suggest?

A

Similar mechanisms have been proposed for 3-D object recognition
• An object is first segmented into a set of basic sub-objects (called geons), and then recognized as a pattern composed of geons

59
Q

what is the grandmother cell hypothesis?

A

If we keep going down the visual information processing pathway, can we eventually find a cell that responds to a very, very, very specific stimulus?

60
Q

what are the weaknesses of the grandmother cell hypothesis?

A

– The final percept of an object is coded by a single
neuron
• However, each neuron’s firing is not so reliable
• If that neuron is lost, our perception of the corresponding
object would be lost
– Perception of novel objects cannot be explained well
– Flexibility of object recognition cannot be explained
well

61
Q

what is ensemble coding in the grandmother cell hypothesis?

A

Object recognition results from the firing of an ensemble of cells (ensemble coding)

62
Q

what has more recent evidence suggested about ensemble coding?

A

– More recent evidence suggests that grandmothercell-
like neurons might exist (Quiroga et al., 2005)
– But not necessarily in the visual object recognition
system per se

63
Q

What is bottom up processing?

A

A? or H?

When the word CAT is presented by the top of the A is cut off to look like a H

64
Q

What is top-down processing?

A

recognising the entire word as CAT even though it is presented with the top of the A is cut off to look like a H

65
Q

what is the word-superiority effect?

A

Superior recognition of letters in a word context
than alone
– Indicates top-down influence on pattern recognition

66
Q

what is the phoneme-restoration effect?

A

Participants were presented with the sentence:
“The state governors met with their respective
legi…latures convening in the capital city.”

Where the … is 120 ms tone prelaced ‘s’

• Only 1 in 20 participants reported hearing this
tone
– And this one participant was unable to locate the tone correctly

PYB204 (10 decks)

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