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Lecture 4

PSY100H1 Lecture Notes - Lecture 4: Necker Cube, Neural Oscillation, Visual Cortex

Course Code
Connie Boudens

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Lecture 4 - 01-28-12
From last week....
The Visual System
lower sensitivity
lower acuity
colour blind
periphery of retina
higher sensitivity/acuity
colour sensitive
in fovea
There is a blind spot. Our brain fills in the blank perceptually.
A series of neurons communicates information from the retina to the cortex
in the eye:
Ganglion cells and optic nerve (goes from eyeball, where the blind spot is, and carries
information to different parts of the brain)
in thalamus:
in cortex
V1, primary visual cortex

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There's some neural activity in the individual system in that visual system diagram. One's a
bright stimulus and one is dull. It can excite or not excite. If we think of two images coming in,
cell B has information coming in from both cell A and C where cell C is only getting information
from cell B, cell D would not have information coming in. This is what elicits one of our optical
illusions i.e. Mach bands, lateral inhibition between neighbouring cells and the retina. Because
the two pieces of information are coming into your visual stream, there's some inhibition going
on in between your cells, it is trying to find the edges to make the perception of the white band
look darker than it actually is. The other example, the checkerboard with the cylinder, square B
is the same level of darkness as A. There's also a shadow coming from the cylinder that
compensates for the darkness as well.
Single-cell recording
the frequency of the action potential are recorded as different stimuli presented to a subject.
Researchers can manipulate what's being shown and record how they fire. What makes them
fire? There are studies involving animals, there are certain cells firing in the brain.

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There's this receptive field. The main thing is that in the RF, there's a center and surround.
When something is stimulated in the centre, the neural firing frequency increases from normal.
When something is in the surround, it actually inhibits/decreases from normal firing. How is this
all related?
The receptive field of the V1, they are related to line orientation. These kind of cells are edge
detectors. Flat, no stimulus, when it's an actual angle, there's more activity, when it's upright,
there's lot of activity.
Different neurons in V1 are specialized, resulting in parallel processing, not serial processing.
Parallel processing in the visual pathway:
P (parvocellular) Cells
M (magnocellular) cells
The what system:
Identification of objects
Occipital-temporal pathway
Visual agnosia
The where system:
locations of objects and guiding our responses
Occipital-parietal pathway
Problems with reaching for seen objects
Binding problem is how do we recognize this as one single unit when you have so much
information coming in from many areas. While things are firing about one particular object, it'll
also be firing about the movement. Our brain interprets that synchrony as coming from one
object, this is the neural synchrony. The systems themselves, the spatial position, the visual
areas that are processing these features - like shape and colour - know that spatial position of
the object. You can think of the coordinates on your GPS. Attention is also critical for the binding
of visual features. When attention is overloaded, people will make conjunction errors. E.g.
recognizing the colour and letter while concentrating on other tasks, you may mix up the
colours, that's the idea of overloading the visual stream (attention is overloaded), this is the idea
of conjunction errors.
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