Lecture 23 Flashcards
Normal
Most cells in visual cortex can be stimulated by light in either eye because for most of the visual field, light from an object reaches corresponding spots on both retinas. So most cortical cells become binocular as the two eyes are stimulated by experience.
Monocular Deprivation
When one eye is closed in development, it quickly loses its connection to visual cortex. If deprived long enough, the animal will become blind in that eye. Similar deprivation in adulthood has virtually no effect on the connections from the eye or the ability of the cat to see.
-Lazy eye= one eye takeover the other = cover strong eye
One Eye Deviation
If the two eyes are not aligned properly, then light from the visual field may still reach both eyes, but it does not reach the corresponding parts of the two retinas. So each cortical cell comes to listen to only one eye or the other. This cat will have very poor depth perception.
Binocular Deprivation
Ironically, briefly depriving both eyes during development may have less of an effect on the connections from the eye to the cortex than depriving one eye. The reason is that the two eyes are still evenly matched in their competition for connections to the cortex. However, prolonged binocular deprivation in development will lead to total blindness.
-Remains somewhat similar to when both eyes are open
Retrograde Degeneration of Visual Tracts
The loss of retinal ganglion cells occurring upstream from a posterior visual pathway lesion
-Starts at cortex and goes all the way to eyes
-Function starts dying off
-Immature visual cortex
Neuroimaging of Visual Deprivation
-Blind have more activation in visual cortex than the sighted
-Visual cortex taken over by other senses
-Grey + white matter reduced in congenital blind people
Rewiring the Brain
-Primary cortices are anatomically and functionally very similar before maturation
-Able to rewire brain so hamster’s auditory cortex uses visual information
-Respond to bot stimulations
Tactile Perception in the Blind
The blind appear to be better than the sighted on certain of these tasks, perhaps as a result of their specific tactile experience, but many of these tasks potentially involve non-spatial cues, and the impact of early versus late blindness, and of Braille-reading experience, remain uncertain
-More nightmares + dream more in hearing and touch
Braille Reading
Visual cortex lights up
- vs. other tactile tasks, doesn’t light up
TMS of the Visual Cortex
Induces tactile sensations
-The age of blindness
-The behavioral importance of the tactile task
The performance as well as the anatomical and functional changes in blind individuals depend on…
-The ventral pathway for the physical properties of tactile stimuli
-The dorsal pathway for the perception of movement
The two major visual pathways are preserved in people born blind and they take over tactile functions…
Auditory Perception in the Blind
Early blindness results in an enhanced ability to hear moving objects in noisy backgrounds
Odor Perception in the Blind
Olfactory threshold was found to be better (perception at lower concentrations) in the blind group, and blind participants significantly outperformed normal sighted controls also in olfactory discrimination test as well as considering the total score
-Recognize people they know
-Recognize strong/dangerous smells
-Increased occipital activation
-Blind better with negative odors
-Woman could smell Parkinson’s Disease?
Taste Perception in the Blind
Only perception that is not better in the blind
-Less exposure
-Overall better with orthonasal but not retronasal
-0 activity in visual cortex
Thermal and Pain Perception in the Blind
Lower pain thresholds to cold and heat in blind participants
-Blind detect way better than we do + react faster
-In C fibers only, not A-Delta fibers
-The age of blindness
-The behavioral significance of the stimulus
Performance, as well as anatomical + functional changes in blind individuals, depend on…
preserved in individuals born blind
Despite degeneration of the visual pathways, the structural and functional skeleton of the visual cortex is…
intermodal plasticity and is often correlated with increased performance
Visual cortex activity is indicative of…
Two hypotheses of Crossmodal Plasicity
-Cortical Reorganization
-Unmasking
Cortical Reorganization
Crossmodal brain responses ae mediated by the creation of new pathways in the brain deprived of a sensory input
Unmasking
The loss of sensory input induces disinhibition and the strengthening of existing neural connections
Sensory Substitution
A technology that aims to compensate for a perceptual disability by substituting one sense for another. In other words, the operation of sensory substitution consists of transmitting through a functional sensory channel a code usually processed by another sensory modality. More concretely, it involves allowing access to information and a phenomenology specific to a perceptual modality through sensory organs that are not specific to this modality
-Use another sense to take over
-E.g. read by touching = braille
Tongue Display Unit
Sensory substitution using tongue (for blind)
-Paul Bach-y-rita
-Seeing what’s on camera through tongue
-Tongue to visual cortex
