PSYC 211 Lecture 8 - Vision (Part 1)

Comprehensive vocabulary flashcards covering the visual system, sensory transduction, optics, photopigments, retinal circuitry, color perception, and visual pathways from PSYC 211 Lecture 8.

Sensation

The detection of a physical stimulus by early sensory pathways, wherein cells of the nervous system transduce external signals into a change in membrane potential and neurotransmitter release.

Perception

The conscious experience and cognitive interpretation of sensory information.

Sensory Neurons

Specialized cells that detect specific physical events, such as molecules, physical pressure, temperature, pH, or visible light.

Visible Light

A narrow portion of the electromagnetic spectrum with wavelengths between $380$ and $750\,\text{nm}$ that can be detected by photoreceptors in the eye.

Ionizing Radiation

High-energy electromagnetic radiation capable of knocking an electron out of an atom, leaving behind positively charged ions that are highly reactive and detrimental to biological processes.

Photoreceptor Cells

Sensory cells in the retina that transduce the energy of visible light into changes in membrane potential, releasing neurotransmitter in a graded fashion without firing action potentials.

Retinal

A light-absorbing photopigment molecule synthesized from vitamin A that changes its 3-dimensional configuration upon absorbing a photon of visible light.

Opsins

Light-sensitive, metabotropic receptor proteins embedded in photoreceptor membranes that bind retinal and trigger an intracellular G-protein signaling cascade when retinal absorbs light.

Rhodopsin

The photopigment protein expressed exclusively in rod cells that is $100\times$ more sensitive to light than cone opsins and is not involved in color vision.

Trichromatic Coding

The principle that color perception is determined by the relative rates of activity (ratio of activation) across three distinct types of cone photoreceptors.

Blue Cone Opsin

A cone opsin protein maximally sensitive to short wavelengths of visible light, peaking at approximately $430\,\text{nm}$.

Green Cone Opsin

A cone opsin protein maximally sensitive to medium wavelengths of visible light, peaking at approximately $535\,\text{nm}$.

Red Cone Opsin

A cone opsin protein maximally sensitive to long wavelengths of visible light, peaking at approximately $575\,\text{nm}$.

Brightness

The perceptual dimension of light that corresponds to the intensity or total amount of electromagnetic energy present.

Hue

The perceptual dimension of light that denotes the principal perceived color, determined primarily by the dominant wavelength.

Saturation

The perceptual dimension of light indicating color purity based on wavelength mixture, where $0\%$ saturation indicates an equal mixture of all wavelengths (grayscale).

Protanopia

A form of red-green color vision deficiency occurring in $1\%$ of males, caused by the complete absence of functional red cone opsin.

Deuteranopia

A form of red-green color vision deficiency occurring in $1\%$ of males, caused by the complete absence of functional green cone opsin.

Tritanopia

A rare color vision deficiency affecting approximately $1\%$ of the population, caused by the complete absence of functional blue cone opsin.

Cone Monochromacy

A condition resulting in the complete absence of color vision because only one of the three cone opsin types is functional.

Achromatopsia

A complete lack of color vision resulting from a functional disruption in the intracellular signaling cascade shared by all cone cells.

Cornea

The transparent front outer layer of the eye that provides a fixed refractive focusing of incoming light.

Iris

A pigmented, contractile ring of muscle that regulates pupil diameter to control the amount of light entering the eye.

Lens

A transparent, layered ocular structure that dynamically changes shape to adjust focus between near and distant objects.

Fovea

The central region of the retina containing a high density of cone photoreceptors and a 1:1 ratio with ganglion cells, enabling high visual acuity ($20/20$) and color vision.

Optic Disk

The site on the retina where ganglion cell axons exit to form the optic nerve and blood vessels enter and leave, creating a physiological blind spot devoid of photoreceptors.

Saccadic Eye Movements

Rapid, jerky shifts in gaze that quickly relocate fixation from one visual target to another.

Pursuit Movements

Smooth, slow ocular movements made to continuously track and maintain focus on an object moving relative to the observer.

Bipolar Cells

Retinal interneurons that receive graded inputs from photoreceptors and relay visual signals forward to retinal ganglion cells.

Retinal Ganglion Cells (RGCs)

The output neurons of the retina that generate action potentials and send their axons through the optic nerve to the brain.

Lateral Geniculate Nucleus (LGN)

A thalamic nucleus that receives visual input from retinal ganglion cells and projects to the primary visual cortex (area V1) in the occipital lobe.

Superior Colliculi

Midbrain structures receiving retinal inputs that coordinate rapid, visually guided reflexive eye and head movements in response to unexpected stimuli.

Predictive Coding Theory

A sensory processing model suggesting that top-down predictions cancel out expected bottom-up sensory signals, transmitting only ascending prediction error signals to guide learning.