Blue= rods Green = Cones
... • V1 appears to be organized into modules
• Each module receives input from both eyes about
one small part of the visual field
• Input from each eye is separated into “ocular
dominance columns” within the module
• CO Blobs: color and low spatial frequency
• Outside of CO Blobs: orientation, movement ...
Visual pathways cortical and sub
... inability to reach for food in slots of different orientation
Electrophysiological studies in monkeys
1970s Mountcastle & Hyvarinen
electrophysiological recordings from dorsal stream neurons
neurons that fire during reaching
neurons firing during saccades towards stationary objects
neurons respondin ...
Visual Awareness - People.csail.mit.edu
... our present knowledge of the visual system.
The first is how much we already know—by
any standards the amount is enormous… The
other surprising thing is that, in spite of all this
work, we really have no clear idea how we
Visual Field and the Human Visual System
... PET Activations of Word vs. Nonword
Brain shows much greater activation
as subjects look at visual words (2nd
row) than when they view a static
fixation point (top row).
After leaving the retina, the outputs of each eye are split
... • Bars of light must be oriented correctly, but can appear anywhere in
the receptive field
• Moving the bar through the field produces a sustained response
• Complex cells often show direction-selectivity:
– they fire more when the bar moves in one direction, and are
suppressed by motion in the oppo ...
Visual System - UAB School of Optometry
... ‘BLINDSIGHT’: preservation of very limited ability to perform
visually guided tasks after destruction of the retina to LGN to
cortex pathway, in the apparent absence of conscious
Bottom line: take out the LGN-cortical system and you are for all
practical purposes completely blind. Les ...
From visual field to V1
... of the M and P layers. K cells are functionally and
neurochemically distinct from M and P cells and
provide a third channel to the visual cortex.
lgn - cinpla
... The lateral geniculate nucleus (LGN) is placed in a prominent position in the early visual pathway. It sits between the retina and the visual cortex, acting
as a relay between the two. Inserting a microelectrode into the LGN reveals that the receptive fields are very similar to those in the retina. ...
Visual System Part 1 – Visual Perception
... • filters, decompresses and restructures the signals from
the retina into a more distributed, temporally precise code
• favours strong synchronous inputs, and often produces
... Note that layer 3 receives input from the left eye and layer 4 receives input from the right eye.
Registration refers to the fact that the projections of activity in layers 3 and 4 are at the same place in their
respective layers, even though the stimulation is from different eyes.
That is, the acti ...
... In the visual search task participants are asked to
report the presence or absence of a target stimulus
among various numbers of distracter stimuli.
If the distracter stimuli differ by a single feature you
usually find the “pop-out” effect: the RT to detect the
target is independent of the numbe ...
Perception - UBC Computer Science
... • Eye Movement
• Visual Attention, Searching, and System
• Reading From the Iconic Buffer
• Neural Processing, Graphemes and Tuned
... Analysis of Visual Information: Role of the Association Cortex
Two Streams of Visual Analysis
• The outputs of the striate cortex (area V1) are sent to area V2, a region of the extrastriate
cortex just adjacent to V1. As we saw in Figure 6.28, a dye for cytochrome oxidase
reveals blobs in V1 and th ...
... LGN interneurons make only local connections.
There are more interneurons than relay neurons!
LGN neurons get feedback connections from cortex. (The
one-way connection from retina to rest of brain is unique in
the visual system).
LGN gets other inputs as well. For example: from brainstem
and perigen ...
Visual Field Defects - Northwestern Medical Review
... however, true of the visual system. Unilateral damage
to the visual cortex is manifested by characteristic
partial loss of vision in both eyes. Neither of the eyes is
able to see the contralateral visual field with respect to
the location of lesions. As we will see later this unique
pattern also hol ...
... some days are better than others. Visual functioning
can even change from hour to hour with some
Visual field defects may also be associated with CVI
due to specific neurological damage.
Movement cues, especially in the peripheral fields can
often stimulate a visual response. Visual in ...
What is Graphic Design?
... • “Personalities” of type
– Formal and informal fonts
– Consequences and font choices
• Consider effect of font choice
• Personality and appropriateness
Top 10 Bizarre Case Studies
... The perception of pain is highly paradoxical in nature. It’s tough to live ‘with’ and it’s tough to
live ‘without’. It’s funny how an experience that seems in every respect to be so bad is, in fact,
extremely important for our survival. Pain is needed because it warns us to stop engaging in
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... We can discriminate visual objects at multiple levels, from coarse categorization to individual
identification. It is not known how the brain adapts to the varying levels of discrimination required in
different behavioral contexts. In the present study, we investigated whether the stimulus selectivi ...
... shortest distance by which 2 lines can be separated & still be
perceived as 2 lines
•Snellen letter charts
designed so that the height of the letters in the smallest line a
normal individual can read at 20 ft (6m) subtends a visual angle of 5
•Jaeger’s cards test for near vision (reading)
Blindsight is the ability of people who are cortically blind due to lesions in their striate cortex, also known as primary visual cortex or V1, to respond to visual stimuli that they do not consciously see. The majority of studies on blindsight are conducted on patients who have the ""blindness"" on only one side of their visual field. Following the destruction of the striate cortex, patients are asked to detect, localize, and discriminate amongst visual stimuli that are presented to their blind side, often in a forced-response or guessing situation, even though they don't consciously recognise the visual stimulus. Research shows that blind patients achieve a higher accuracy than would be expected from chance alone. Type 1 blindsight is the term given to this ability to guess—at levels significantly above chance—aspects of a visual stimulus (such as location or type of movement) without any conscious awareness of any stimuli. Type 2 blindsight occurs when patients claim to have a feeling that there has been a change within their blind area—e.g. movement—but that it was not a visual percept. Blindsight challenges the common belief that perceptions must enter consciousness to affect our behavior; it shows that our behavior can be guided by sensory information of which we have no conscious awareness. It may be thought of as a converse of the form of anosognosia known as Anton–Babinski syndrome, in which there is full cortical blindness along with the confabulation of visual experience.