Transcript Tine 1 Vision Review.pptx

MENTAL REPRESENATIONS
Neur 3680 Midterm I review
Mental Representations
• Mental representations can start with sensory
input and progress to more abstract forms
– Local features such as colors, line orientation,
brightness, motion are represented at low levels
A “labeled line”
-Activity on this unit “means” that a
line is present
-Does the line actually have to be
present?
Mental Representations
• Mental representations can start with sensory
input and progress to more abstract forms
– Local features such as colors, line orientation,
brightness, motion are represented at low levels
A “labeled line”
-Activity on this unit “means” that a
line is present
-Does the line actually have to be
present?
texture defined boundaries are representations arrived at by
synthesizing the local texture features
the representation is embellished and extended
Mental Representations can be transformed
SAME
MIRROR-REVERSED
Mental representations
• Posner letter matching task
– Same category or different?
– Physically the same?
• Stroop task
– interference
First Principles
•
What are some ways that information might be represented by neurons?
– Magnitude might be represented by firing rate (e.g. brightness)
– Presence or absence of a feature or piece of information might be represented by
whether certain neurons are active or not – the “labeled line” (e.g. color,
orientation, pitch)
– Conjunctions of features might be represented by coordinated activity between
two such labeled lines
– Binding of component features might be represented by synchronization of units in
a network
Posner and his colleagues had participants view two letters and
respond according to whether these letters were both vowels,
both consonants, or one of each. Participants were fastest when
viewing two physically identical letters, somewhat slower when
viewing the same letter in two different fonts, and slowest in the
case where two different consonants were presented. This
finding shows that
a.
b.
c.
d.
we form multiple representations of stimuli.
we form representations of stimuli based only on their
physical attributes.
we form representations of stimuli based only on their
abstract category membership.
more complex mental representations produce faster
reaction times.
Posner and his colleagues had participants view two letters and
respond according to whether these letters were both vowels,
both consonants, or one of each. Participants were fastest when
viewing two physically identical letters, somewhat slower when
viewing the same letter in two different fonts, and slowest in the
case where two different consonants were presented. This
finding shows that
a.
b.
c.
d.
we form multiple representations of stimuli.
we form representations of stimuli based only on their
physical attributes.
we form representations of stimuli based only on their
abstract category membership.
more complex mental representations produce faster
reaction times.
VISION
Neur 3680 Midterm I review
Visual Pathways
• Image is focused on the retina
• Fovea is the centre of visual
field
– highest acuity
• Peripheral retina receives
periphery of visual field
– lower acuity
– sensitive under low light
Retina has distinct layers…
LGN
signals converge onto ganglion cells which send
action potentials to the (LGN)
•two kinds of ganglion cells:
•Magnocellular and Parvocellular
Amacrine and bipolar cells perform “early”
processing
converging / diverging input from receptors
lateral inhibition leads to centre/surround
receptive fields - first step in shaping “tuning
properties” of higher-level neurons
Photoreceptors:
•Rods and cones respond
to different wavelengths
RETINA
Lateral Geniculate Nucleus maintains
segregation:
of M and P cells (mango and parvo)
of left and right eyes
Primary visual cortex receives input from LGN
Primary cortex maintains distinct pathways –
functional segregation
M and P pathways synapse in different layers
The Role of “Extrastriate” Areas
1. System is hierarchical
2. System is analytic and parallel
SUMMARY:
Retina
Dorsal stream
area MT
Ventral stream
V4
M cells-interblobs
LGN
V1
P cells- blobs
SUMMARY:
movement and
direction
Dorsal stream
Retina
area MT
WHERE/HOW
V4
WHAT
M cells-interblobs
LGN
V1
P cells- blobs
Ventral stream
color
Zeki et al.
Subtract Voxel
intensities during
these scans…
…from voxel
intensities during
these scans
…etc.
Time ->
The receptive fields in the primary visual cortex are
________ the receptive fields in the visual association
areas.
a.
b.
c.
d.
smaller than
larger than
equal in size to
less selective than
The receptive fields in the primary visual cortex are
________ the receptive fields in the visual association
areas.
a.
b.
c.
d.
smaller than
larger than
equal in size to
less selective than
The term ________ is used to describe the situation in which
group 1 is impaired on task X and unimpaired on task Y and
group 2 is impaired on task Y and unimpaired on task X. In
contrast, the term ________ is used when group 1 is
impaired on task X and unimpaired on task Y and group 2 is
unimpaired on both tasks X and Y.
a.
b.
c.
d.
single dissociation / double dissociation
double dissociation / single dissociation
double dissociation / triple dissociation
triple dissociation / double dissociation
The term ________ is used to describe the situation in which
group 1 is impaired on task X and unimpaired on task Y and
group 2 is impaired on task Y and unimpaired on task X. In
contrast, the term ________ is used when group 1 is
impaired on task X and unimpaired on task Y and group 2 is
unimpaired on both tasks X and Y.
a.
b.
c.
d.
single dissociation / double dissociation
double dissociation / single dissociation
double dissociation / triple dissociation
triple dissociation / double dissociation
Zeki et al.
Stroke = Achromatopsia
Subtract Voxel
intensities during
these scans…
…from voxel
intensities during
these scans
…etc.
Time ->
Subtract Voxel
intensities during
these scans…
MOVING
…from voxel
intensities during
these scans
STATIONARY
MOVING
Time ->
STATIONARY
…etc.
Stroke = akinetopsia
Subtract Voxel
intensities during
these scans…
MOVING
…from voxel
intensities during
these scans
STATIONARY
MOVING
Time ->
STATIONARY
…etc.
Visual Neuron Responses
•
This conceptualization of the visual system was “static” - it did not take into account the
possibility that visual cells might change their response selectivity over time
–
Logic went like this: if the cell is firing, its preferred line/edge must be present and…
–
if the preferred line/edge is present, the cell must be firing
•
We will encounter examples in which neither of these are true!
•
Representing boundaries must be more complicated than simple edge detection!
EDGES
•Colour
•Brightness
•Texture
•Motion cues
•Depth cues
The distinct modes of vision offered
by feedforward and recurrent
processing
Victor A.F. Lamme and Pieter R.
Roelfsema
Dichotomies:
Dorsal vs. Ventral stream
- spatial and object vision
Pre-attentive vs. Attentive
Conscious vs. Unconscious
The Feed-Forward Sweep
• The feed-forward sweep is the initial response
of each visual area “in turn” as information is
passed to it from a “lower” area
• Characteristics:
– a single spike per synapse
– no time for lateral connections
– no time for feedback connections
The Feed-Forward Sweep
• The feed-forward sweep is the initial response
of each visual area “in turn” as information is
passed to it from a “lower” area
• Characteristics:
– a single spike per synapse
– no time for lateral connections
– no time for feedback connections
Curve tracing
– monkey indicates whether a particular
segment is on a particular curve
– requires attention to scan the curve and
“select” all segments that belong together
– that is: make a representation of the entire
curve
– takes time
What is the binding problem?
QUESTIONS: