Sensation/perception 2.0

the eye and neural pathways, primary visual cortex

What are the two basic processes of the eye?

First, the cornea, pupil and lens focus light on the retina. Next, the retina transduces this visual image into neural impulses that are relayed to and interpreted by the brain.

What is the role of the pupil and iris?

The pupil controls how much light enters the eye. The iris adjusts the pupil’s size by dilating or constricting.

What is the retina and what does it do?

The retina is a light-sensitive layer that converts light into neural impulses (transduction) and sends them via the optic nerve to the brain.

rods and cones functions

rods (which produce sensations in black, white and grey and are very sensitive to light) and cones (which produce sensations of colour)

Where are rods and cones located?

• Rods: concentrated in the periphery of the retina.

• Cones: concentrated in the fovea, the central part of the retina.

How are rods and cones connected to the brain?

Light passes through layers of neurons to reach photoreceptors, called rods and cones, which respond to different wavelengths of light. These receptors in turn connect to bipolar cells, which pass information to the ganglion cells, whose axons form the optic nerve.

What happens after photoreceptors bleach in the retina?

They excite bipolar cells, which then stimulate ganglion cells to fire.

What are the optic tracts?

Continuations of the optic nerve axons carrying combined information from both eyes after the optic chiasm.

how does visua information go from teh optic nerve to the brain

From the optic nerve, visual information travels along two pathways. One is to the superior colliculus in the midbrain, which in humans is particularly involved in eye movements. The other is to the lateral geniculate nucleus in the thalamus and on to the visual cortex.

How does blindsight relate to the two visual pathways?

Visual processing in the superior colliculus and lateral geniculate nucleus can guide behavior even without conscious vision.

What is blindsight?

A condition where people with damage to the primary visual cortex deny seeing objects but can respond to them accurately without conscious awareness.

feature detectors

Feature detectors in the primary visual cortex respond only when stimulation in their receptive field matches a particular pattern or orientation.

what are the what and where pathways

Beyond the primary visual cortex, visual information flows along two pathways, the ‘what’ pathway (involved in determining what an object is) and the ‘where’ pathway (involved in locating the object in space, following its movement and guiding movement towards it).

Young–Helmholtz, or trichromatic, theory

operates at the level of the retina. Young–Helmholtz, or trichromatic, theory, the eye contains three types of receptors that are most sensitive to wavelengths experienced as red, green or blue.

opponent-process theory

According to opponent-process theory, the colours we experience (and the after-images we perceive) reflect three antagonistic colour systems; a blue–yellow, red–green and black–white system. operates at higher neural levels.