Ch 12: identifying stimuli and stimulus objects Flashcards
Grandmother cell coding scheme vs population coding scheme
- Grandmother cell coding scheme:
- there is one neuron dedicated to identifying each possible stimulus object. - Population coding scheme:
- seeing an object activates a specific COMBINATION of neurons that collectively represent the object.
- some of these neurons might also be active when you see a different stimulus.
- the code does not reside in the activity of the individual neurons but in their combination.
____ ___ is the pathway that uses spatial information to guide eye, head, and hand movements.
____ ___ is the pathway concerned primarily with object identification
DORSAL STREAM is the pathway that uses spatial information to guide eye, head, and hand movements.
VENTRAL STREAM is the pathway concerned primarily with object identification
dorsal and ventral streams both originate from ___
V1
The dorsal stream originates in the ___ of the ___ lobe and then passes through the ___ ___ ___ to the ___ and __ cortices
The dorsal stream originates in the V1 of the OCCIPITAL lobe and then passes through the POSTERIOR PARIETAL CORTEX to the PREMOTOR and MOTOR cortices
The ventral stream proceeds from __ to the inferior portion of the ___ ___
The ventral stream proceeds from V1 to the inferior portion of the TEMPORAL LOBE
how do on-center retinal ganglion cells respond to bright spots presented at the center of their spatial receptive field?
by increasing in firing rate
How do on-center retinal ganglion cells respond when they are stimulated with a ring of light surrounding the center of their receptive field?
they lower their firing rates
stimulating on-center retinal ganglion cells with uniform light yields what response?
no response (no change in firing rate)
off-center retinal ganglion cells respond with increased firing rates to:
dark spots in the receptive field’s center
on- and off-center ganglion cells receive input from:
ON and OFF bipolar cells
surround cone inhibitory influence is due primarily to retinal ____ cells
surround cone inhibitory influence is due primarily to retinal HORIZONTAL cells
the input from photoreceptors onto horizontal cells is _____, whereas the output of horizontal cells back onto photoreceptors is ______
the input from photoreceptors onto horizontal cells is EXCITATORY, whereas the output of horizontal cells back onto photoreceptors is INHIBITORY
What generates the center-surround organization and what is its purpose?
LATERAL INHIBITION (surround inhibition) through HORIZONTAL CELLS generates the center-surround organization. It SHARPENS LOCAL STIMULUS CONTRAST
Our visual system is more sensitive to ___ luminance contrast than to ___ luminance
Our visual system is more sensitive to LOCAL luminance contrast than to ABSOLUTE luminance
Significance of Mach bands
-at the boundary between luminance intensites, the lighter coloured square seems to be even brighter and the darker square seems to be darker in colour.
-this is because lateral inhibition enhances the contrast when there are zones of different intensities
(light edge on dark square, dark edge on light square)
which brain region provides the major visual input to V1?
Lateral geniculate nucleus (LGN)
The LGN has ___ distinct layers
6
Do V1 neurons respond better to lines and edges or to circular spots?
lines and edges
V1 simple cells respond best to lines presented at a ___ ____ and in a ____ ____
V1 simple cells respond best to lines presented at a SPECFIC LOCATION and in a PARTICULAR ORIENTATION
What did Hubel and Wiesel hypothesize what the reason V1 cells become sensitive to lines rather than spots?
They hypothesized that each simple cell receives CONVERGING INPUT from multiple geniculate neurons whose receptive field centers are ALL THE SAME TYPE and ARRANGED IN A LINE
If the receptive fields of the geniculate neurons converging on a V1 neuron are all of the ON-CENTER type, then…
the V1 simple cell should respond to a BRIGHT line that falls across those on-centers
If the receptive fields of the geniculate neurons converging on a V1 neuron are all of the OFF-CENTER type, then…
the V1 simple cell should respond best to a DARK line tht covers those off-centers
direction sensitivity is generated mainly in the __ __
visual cortex
V1 Simple vs complex cells
- both respond preferentially to bright or dark lines and edges in a particular orientation
- complex cells receive converging input from multiple V1 simple cells
- complex cells respond to activity in any of their converging input lines, whereas simple cells fire only when a particular combination of geniculate neurons is excited
Sine-wave grating
a series of parallel bands varying continuously in brightness according to a sine-wave function, along a line perpendicular to their lengths
Spatial frequency
the relative width of the bands in a sine-wave grating, measured in cycles per degree of visual angle
the visual angle between adjacent sine waves is ___ when the waves are closer together
smaller
Although Hubel and Wiesel’s studies suggested that neurons in V1 detected lines and edges, subsequent research found that they actually responded best to ________
sine-wave gratings
what is the spatial frequency of a sine-wave grating?
its variation in brightness measured in cycles per degree of visual angle
small objects, details within large objects, and large objects with sharp edges provide a signal rich in ___ ______
high frequencies
large areas of light and dark are represented by __ ___
low frequencies
most important visual information is that contained in ___ spatial frequencies
low
how does ISOI work?
Intrinsic signal optical imaging (ISOI) measures changes in tissue oxygenation.
Oxygenated and deoxygenated blood absorb light differently.
Orange light directed at animal’s exposed cortex.
ISOI measures dip in blood oxygenation due to neural activity.
images are taken
aperture problem
- seen in neurons with a SMALL receptive field
- When looking at a moving straight line through an aperture, the edge always seems to move at right angles to its long axis, regardless of the underlying object’s true direction of motion
How can the aperture problem be solved?
by combining info from multiple neurons
ie. multiple edges in multiple apertures
Results from the monkey experiment where their MT cells were stimulated
-monkeys failed to identify the movement direction correctly when the preferred direction of the stimulated neurons differed from that of the dots that were presented.
THE ELECTRICAL STIMUATION BIASES THE MONKEY’S PERCEPTION OF MOVEMENT DIRECTION IN FAVOR OF THE DIRECTION TO WHICH THE STIMULATED NEURONS ARE TUNED AND AGAINST THE OPPOSITE DIRECTION
MT in “MT neurons” stands for
middle temporal
Red-green opponent cells compare the activation levels of __ and ___ cones
L- and M-cones
blue-yellow opponent cells compare the activity if the __ cones to the combined activity of the __ and __ cones
blue-yellow opponent cells compare the activity if the S-cones to the combined activity of the L- and M-cones
bottom-up vs top-down spatial attention
bottom-up: something captures your attention
top-down: looking towards an area to see if something is happening
double opponent cells
give opposite responses to opposite wavelengths in center vs. surround
the phenomenon that perception of colour barely changes as it gets darker is called
color constancy
colour-sensitive patches in the anterior occipital and posterior temporal lobes are called ___
globs
what do Face-selective neurons respond to
respond strongly to faces and poorly to scrambles faces or other stimuli. They respond more poorly to faces without eyes than with eyes.
What happens when you electrically stimulate face-selective cells?
perception becomes biased in favour of faces
What is the name of the largest face-selective patch in the inferior portion of the temporal lobe?
fusiform face area
higher neural response for (basic/superordinate) words
basic
Category-sensitive neurons can be found in the:
inferior temporal cortex
what is agnosia?
deficit in object identification
porisipagnosia
inability to identify faces
-problems in conducting in INFERIOR LONGITUDINAL FASCICULUS
cell assembly in the olfactory cortex
repeated exposure to a specific olfactory stimulus forges the olfactory cortex neurons activated by that stimulus into a coherent entity (cell assembly)
different olfactory cortex nerves converge onto a single ___ ___, which diverges onto ___ ___
different olfactory cortex nerves converge onto a single OLFACTORY GLOMERULUS, which diverges onto OLFACTORY EPITHELIUM
the auditory cortex ascends to the neocortex though a series of ___, ____ and ___ nuclei
the auditory cortex ascends to the neocortex though a series of MEDULLARY, MIDBRAIN and THALAMIC nuclei
Whee is gthe auditory cortex?
it lies along the superior edge of the temporal lobe
auditory cortex is divisible into 3 regions:
core, belt, and parabelt regions
What region of the audtory cortex is the primary auditory cortex (A1) part of?
core
when the belt area is damaged, what can it produce?
an auditory agnosia
damage to the left belt results in __ __ and damage in the right belt results in ___
damage to the left belt results in RECEPTIVE APHASIA (ie. Wernicke’s aphasia) and damage in the right belt results in AMUSIA
