PSYC 212: Sensation and Perception in the Blind

Crossmodal Plasticity

The brain's ability to adapt and integrate sensory functions. In the case of congenital blindness, the brain tends to co-opt the extra space

Hubbel and Weisel

Examined a cat's brain and found that there are edge detectors in v1 and that they play a role in orientation (visual deprivation test)

Effect of Prolonged Visual Deprivation

When the eyes are blinded, cells in those areas begin to die off, leading to a different distribution of cells between eyes due to a shift in ocular dominance

Ocular Dominance

The property of the receptive fields of striate cortex neurons by which they demonstrate a preference, responding somewhat more rapidly when a stimulus is presented in one eye than when it is presented in the other.

Types of Ocular Dominance

Normal, monocular deprivation, bionocular deprivation, one-eye deviated

Critical Region

During visual deprivation, there is a critical period of readjustment where increased GABA signaling increases plasticity, generally between the 21st and 35th day.

Long-Term Effect of Visual Deprivation on Ocular Structures

Leads to retrograde degeneration of visual tracts due to inactivity and an immature visual cortex, increased metabolism of the visual cortex, a reduction in brain volume, and a thicker cortex

Neural Activity in the Visual Cortex of the Blind

Blind individuals have more activity in the visual cortex than sighted people, as that space is co-opted by the brain for other functions

Primary Sensory Cortices Plasticity

These areas are highly adaptable and reprogrammable before maturation, as demonstrated in the hamster lesion experiment

Sensory-Impaired Enhancements

In the congenitally impaired, other senses are heightened

TMS (transcranial magnetic stimulation)

The use of strong magnets to briefly interrupt normal brain activity as a way to study brain regions and see what lights up

Performance changes in the Blind

Depends on the age of blindness and behavioral importance of the tactile task needed

Visual Stream Preservation

Dorsal and Ventral visual streams are preserved even in blindness, but the ventral takes over processing physical properties of tactile stimuli, and the dorsal visual stream takes over the perception of movement

Heightened Senses in the Congenitally Blind

Heightened audition can allow for the use of echolocation, olfaction allows for scent-based identification or emotional sensation, touch is heightened, and taste remains the same

Thermal and Pain Perception in the Blind

a-delta and c-fibers are still used, with blind people detecting c-fibers much better and faster, with no change in a-delta because it's priority comes from visual perception

Crossmodal Plasticity Causes

Cortical re-organization or unmasking hypotheses

Cortical Re-Organization Hypothesis

The creation of new pathways where an inactive brain function is made useful

Unmasking Hypothesis

The loss of sensory input induces disinhibition and the strengthening of existing neural connections

Sensory Substitution

The use of technology to compensate a perceptual disability by subbing in one sense for another, essentially by transmitting a code to channel info handled by an unavailable sense (e.g Braille)

Paul Bakirita Experiment

Experiment to get people to see with their back (example of sensory substitution) (Non-Invasive)

Tongue-Display Unit

With the use of a machine, one can see with taste, induces activity in visual brain region, without training : lines, curves; with training : shapes, rolling balls, traverse mazes, letters. Objects experienced outside the body. The resolution is still poor, but relies on electrical impulses instead of sight. (Non-Invasive)

Cortical Implants on the Visual Cortices

A highly invasive method of sensory substitution that is exactly as painful as it sounds