Lecture 8 Flashcards
What is Helmholtz’s Theory Of Unconscious Inference?
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)
What is the likelihood principle?
we perceive the world in the way that is “most likely”
based on our past experiences
What is Bayesian inference?
It estimates the probability of a given outcome influenced by two factors
What two things influence Bayesian inference?
- The prior probability (our initial belief about the probability of an
outcome) - The likelihood of a given outcome, or the extent to which the available
evidence is consistent with the outcome
What are modules?
some dedicated neural mechanisms that are specialized for processing particular kinds of stimuli (e.g.
the FFA to process faces)
What is prosopagnosia
an inability to perceive faces
Describe inversion effects
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
Describe experience-dependent plasticity
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
Describe the expertise hypothesis
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!)
What is binocular rivalry?
occurs when each eye is
presented with a different image
Describe Tong et. al study
- 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)
What is neural mind reading?
predicting what a person is perceiving or thinking
about based upon their neural activity (typically accomplished using fMRI)
Describe the Kamitani and Tong study
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
What’s the difference between structural and semantic encoding?
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
What is visual scanning?
refers to visually exploring the environment (i.e. looking from
place to place)
describe the process of visual scanning
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
What is covert attention?
attention that is decoupled from your
gaze (e.g. watching something ‘out of the corner of your eye’)
What is visual salience?
areas of stimuli that attract attention due to their physical
properties
Describe a salience map
Various properties relevant for contracting a salience map (e.g. colour,
contrast, orientation, texture, movement, etc)
Describe attentional capture
occurs when particularly salient properties of stimuli
result in rapid and involuntary shifts of attention (e.g. something that stands
out)
Describe the Shinoda study
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!)
Describe Vo and Henderson study
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