Key Concepts in Vision and Perception

Sensation

The act of receiving sensory information (internal or external).

Perception

How the brain assigns meaning to this sensory information.

Electromagnetic spectrum

Light is measured in terms of wavelength and amplitude.

Wavelength

Determines colour.

Amplitude

Determines brightness.

Visible light

A tiny portion of the electromagnetic spectrum.

Cornea

Focuses and places image on retina; transparent (no blood vessels), nourished by anterior and vitreous humour.

Choroid

Blood supply to the eye.

Iris

Muscle that contracts in response to light.

Lens

Transparent, focuses light; changes shape via accommodation.

Retina

Sheet of photoreceptors (rods & cones) at back of eye.

Rods

Low light, brightness, low resolution.

Cones

Colour, daylight, high resolution.

Fovea

High-acuity area rich in cones, at 0° visual angle.

Blindspot

15-18° off-centre, no photoreceptors (optic nerve exits).

Ganglion cells

Axons form the optic nerve (127M receptors → 1M axons).

Visual pathway

Eye → LGN (subcortex) → V1 (primary visual cortex).

Neural implementation

Energy → transduction → neural signal → processing.

Ventral stream

Object identification (V1 → temporal lobe).

Dorsal stream

Spatial location (V1 → parietal lobe).

Retinotopic mapping

2D mapping of retina to LGN and V1.

Receptive field

Part of retina a cell responds to.

Centre-surround architecture

Excitation in the centre, inhibition in the surround.

Lateral inhibition

Enhances contrast; neighbours inhibited by 10%.

Monocular blindness

Severed optic nerve in one eye.

Bitemporal hemianopia

Damage at optic chiasm (nasal retinae affected).

Left homonymous hemianopia

Right-side lesion post-chiasm.

Macular sparing

V1 lesion spares some central vision.

Blindsight

A condition where individuals respond to visual stimuli without conscious visual perception.

How is sensory information implemented neutrally?

1. Sensory organs absorb energy

2. energy is transduce into a neural signal

3.the neural signal is sent throughout the brain where further processing takes place