Biological Psychology: Vision and the Retina

Flashcards covering the transduction of light, retinal anatomy, visual pathways, and the biological basis of vision and circadian rhythms.

Visible spectrum

The narrow range of wavelengths in the electromagnetic spectrum, extending from $380\,nm$ to $760\,nm$, that the human eye is sensitive to.

Hue

The dimension of light colour determined by the wavelength of electromagnetic radiation.

Brightness

The dimension of light colour determined by the intensity of electromagnetic radiation.

Saturation

The dimension of light colour determined by the purity of electromagnetic radiation.

Cornea

The transparent outer layer of the eye through which light enters.

Lens

A structure made of transparent layers behind the cornea that alters its shape to focus images onto the retina.

Vitreous humour

The clear gelatinous fluid that fills the eyeball.

Retina

The light-sensitive structure lining the back of the eye containing photoreceptors, specialized neurons, axons, and dendrites.

Optic disk

The common point where axons from the retina leave the eye; it contains no photoreceptors and creates a blindspot.

Optic nerve

The bundle of axons (the second cranial nerve) that carries visual information from the optic disk to the brain.

Rods

A type of photoreceptor ($120\,million$ per retina) that is highly sensitive to light, used in dim illumination, and lacks sensitivity to colour and fine detail.

Cones

A type of photoreceptor ($6\,million$ per retina) concentrated in the fovea, responsible for colour vision and fine detail in daylight.

Fovea

The central region of the retina responsible for the central few degrees of the visual field, where cones are most concentrated.

Opsin

The protein component of a photopigment molecule.

Retinal

The lipid component of a photopigment molecule.

Rhodopsin

The specific photopigment found in human rods, consisting of rod opsin plus retinal.

Short-wavelength (S) cones

Cones with peak sensitivity at $420\,nm$, responsible for perceiving blue light.

Medium-wavelength (M) cones

Cones with peak sensitivity at $530\,nm$, responsible for perceiving green light.

Long-wavelength (L) cones

Cones with peak sensitivity at $560\,nm$, responsible for perceiving red light.

Deuteranopia

A genetic condition where green cones are absent, leading to red-green colour deficiency.

Protanopia

A genetic condition where red cones are absent, leading to red-green colour deficiency.

Ishihara Colour Plates

A series of disks containing digits used to test for anomalies in colour perception.

Receptive field

The small region of the visual field (or retina) to which a single ganglion cell responds.

ON cells

Ganglion cells excited by light in the centre of their receptive field and inhibited by light in the surrounding field.

OFF cells

Ganglion cells inhibited by light in the centre of their receptive field and excited by light in the surrounding field.

Optic chiasm

The location where axons from the nasal halves of the retinas cross to the opposite hemisphere of the brain.

Lateral Geniculate Nucleus (LGN)

A part of the thalamus containing six layers that receives visual input from the optic nerves and projects to the primary visual cortex.

Magnocellular layers

The inner two layers of the LGN containing larger cell bodies, part of a system for analyzing specific visual information.

Parvocellular layers

The outer four layers of the LGN containing smaller cell bodies.

Suprachiasmatic nucleus (SCN)

A region of the hypothalamus that acts as a biological clock, using light information to entrain circadian rhythms to a 24-hour cycle.

Melanopsin ganglion cells

Specialized ganglion cells that convey light information to the SCN to synchronize the biological clock.

Phosphenes

Sensations of light flashes, such as those generated by the microelectrode array in a bionic eye implant.