Problem 2: The visual brain Flashcards
what is the optic chasm
x shaped bundle of nerves, the crossover between the eyes and the hemispheres, which causes each hemisphere to be connected to the eye on the contralateral side of the brain
visual field and contralaterality
visual field is determined by based on where the person is fixating, everything right from the focal points is the right side of the visual field and vice versa, both eyes can see both visual fields
visual pathway
retina –> optic nerve –> optic chimes –> Lateral geniculate nucleus (LGN) (90%) and Superior Colliculus (10%) –> visual cortex
Lateral Geniculate Nucleus
LGN is located in the thalamus and regulates 90% of the info from the retina. purpose is to regulate neural information as it flows from the retina to the cortex, it also inhibits info from the retina
Superior colliculus
other 10% of fibers from the retina, this structure is involved in controlling eye movement
Visual receiving are / Striate cortex / Area V1
signals from LGN travel here, part of the brain where the signals are actually being processed
how is V1 structured?
layers seperate information from right and left eye (LRLRLR), with a centre surround configuration (center is excitatory, surround is inhibitory)
the layers of V1:
-Magnocellular layers (M-cells): large cell bodies, caries info about dynamic visual processes (motion, flicker)
-Parvocellular layers (P-cells): small cell bodies, carries info about color, texture, form and depth
-keniocellular layers (K-cells): very small cell bones
what are simple cells
in V1, they have side by side receptive fields and are responsible for orientation
what are complex cells
in V1, respond to movement (best to a particular direction), like simple cells but + movement
What are end-stopped cells
in V1, fires to moving lines of a specific length or to Cornes and edges
feature detectors
name for simple, complex and end-stopped cells because they fire in response to specific features
what is selective adaptation and how does it work
neurons that react to specific features in times become adapt and fire less when the stimulus is presented again –> less sensitive neurons –> less sensitive perception
what is a contrast threshold
the minimum intensity difference between two adjacent bars that can just be detected
how was selective adaptation measured
first a person’s contrast threshold was determined by letting them look at different orientations of lines, then they showed them a high-contrast line set and let them adapt to it, then they showed them the first contrast lines things and measured firing again –> higher threshold (less sensitive)
the difference between a orientation tuning curve and a psychophysically determined selective adaptation curve
an orientation tuning curve focuses on how a neuron responds to a certain orientation, the psychophysically determined selective adaptation curve shows the adaptation of nerve cells after exposure and is wider because the adapting neurons activates surrounding neurons
what is selective rearing and what is the role of neural plasticity (or experience dependent plasticity)
if an animal is reared in an environment that contains only certain types of stimuli, then neurons that respond to these stimuli will become more prevalent. Neural plasticity is the idea that response properties of neurons can be shaped by perceptual experience. rearing an animal in an environment that only contains vertical lines results in the visual Cortex mainly having simple cells that respond to verticals
how do selective rearing and selective adaptation contradict each other and how does it make sense
it seems to contradict each other because selective adaptation would suggest neurons becoming less sensitive after exposure, while selective rearing would suggest neurons becoming more sensitive. it works together because selective adaptation is short term and selective rearing is long term
V1 is organised into columns, how does that work?
Location columns: column that contains nerves that respond to the same location on the retina, they are positioned perpendicular to the surface of the striate cortex
Orientation columns: alle the location columns are specialised in different orientations, together they make up the orientation columns
Ocular dominance column: preference for one eye
Hypercolumn: a location column with all of its orientation columns in it
Tiling
you location columns cover your entire visual field in an overlapping Tiling manner
Single dissociation
2 groups are tested on 2 tasks and a between-group difference is apparent in only one task (can’t see whether functions are independent)
Double dissociation
demonstration that one task is affected by one type of manipulation, whereas a second task is affected by a different type of manipulation (works both ways –> functions are independent)
