Lecture 8

Question 1

What is Helmholtz’s Theory Of Unconscious Inference?

Answer 1

some of
our perceptions as the result of unconscious assumptions and inferences we
make about the environment based on our prior knowledge and personal
history of experiences (i.e. top-down mechanisms)

Question 2

What is the likelihood principle?

Answer 2

we perceive the world in the way that is “most likely”
based on our past experiences

Question 3

What is Bayesian inference?

Answer 3

It estimates the probability of a given outcome influenced by two factors

Question 4

What two things influence Bayesian inference?

Answer 4

1. The prior probability (our initial belief about the probability of an
   outcome)
2. The likelihood of a given outcome, or the extent to which the available
   evidence is consistent with the outcome

Question 5

What are modules?

Answer 5

some dedicated neural mechanisms that are specialized for processing particular kinds of stimuli (e.g.
the FFA to process faces)

Question 6

What is prosopagnosia

Answer 6

an inability to perceive faces

Question 7

Describe inversion effects

Answer 7

Inversion effects are strong for faces, and are said to occur for stimuli that people
have difficulty noticing unusual details (anomalies) in when turned upside down yet these anomalies are easily and rapidly detected when the stimuli is
right-side up

Question 8

Describe experience-dependent plasticity

Answer 8

Experience-dependent plasticity in
humans can exert a strong effect on
perception

• Brain imaging experiments show areas that
  respond best to letters and words
• fMRI experiments show that training results
  in areas of the FFA responding best to:
• Greeble stimuli
• Cars and birds, for those who have
  expertise in these areas

Question 9

Describe the expertise hypothesis

Answer 9

Observations that developing
expertise in something can lead to
recruitment of the FFA for
associated stimuli supports the
expertise hypothesis (though this
is still controversial!)

Question 10

What is binocular rivalry?

Answer 10

occurs when each eye is
presented with a different image

Question 11

Describe Tong et. al study

Answer 11

• Tong et al. (1998) used binocular rivalry to
  demonstrate that changes in perception and
  changes in brain activity mirrored each other
• When participants reported perceiving the
  house, the PPA was active (and vice versa: the
  FFA was active when perceiving the face)

Question 12

What is neural mind reading?

Answer 12

predicting what a person is perceiving or thinking
about based upon their neural activity (typically accomplished using fMRI)

Question 13

Describe the Kamitani and Tong study

Answer 13

Gratings with different orientations were presented to participants

• Responses from fMRI voxels were measured
• Activity patterns across voxels varies by grating orientation
• An orientation decoder was used to analyze the voxel activity
• The decoder could accurately predict which orientation had been presented

Question 14

What’s the difference between structural and semantic encoding?

Answer 14

Structural encoding: based on relationship between voxel activation and
structural characteristics of a scene (e.g. shapes, lines, textures, etc.)

• Semantic encoding: based on the relationship between voxel activation and the
  meaning or category of a scene

Question 15

What is visual scanning?

Answer 15

refers to visually exploring the environment (i.e. looking from
place to place)

Question 16

describe the process of visual scanning

Answer 16

involves making many fixations, in which we dwell on something to
extract information, which are linked by saccadic eye movements

• This is necessary for high-acuity vision (on account of fovea vision) and we
  typically make about 3 saccades/second
• Represents overt attention

Question 17

What is covert attention?

Answer 17

attention that is decoupled from your
gaze (e.g. watching something ‘out of the corner of your eye’)

Question 18

What is visual salience?

Answer 18

areas of stimuli that attract attention due to their physical
properties

Question 19

Describe a salience map

Answer 19

Various properties relevant for contracting a salience map (e.g. colour,
contrast, orientation, texture, movement, etc)

Question 20

Describe attentional capture

Answer 20

occurs when particularly salient properties of stimuli
result in rapid and involuntary shifts of attention (e.g. something that stands
out)

Question 21

Describe the Shinoda study

Answer 21

Shinoda et al. (2001) measured observers’ fixations during computer simulated
driving while searching for stop signs

• They found participants were more likely to detect stop signs when they were at
  intersections (45% of all fixations were directed at intersections) and often missed
  them when they were placed elsewhere

expectation based on prior knowledge directs their search
behaviour (example of a semantic regularity!)

Question 22

Describe Vo and Henderson study

Answer 22

Found that subjects fixated
objects out of context in their location (e.g. printer in the
kitchen) for longer

Differences in eye movements related to task instructions/goals demonstrates
a modulatory role for top-down processing