Week 3 PSYC 236 Perception and Cognition - Colour Theory

Vocabulary flashcards covering the physiological and psychological aspects of colour perception, including photoreceptors, neural pathways, and colour mixing theories.

Trichromacy

The theory that the human visual system uses three different types of cones ($S$, $M$, and $L$) to perceive the full spectrum of colour.

S-cone

A short-wavelength sensitive photoreceptor with a peak sensitivity at approximately $420\,nm$.

M-cone

A medium-wavelength sensitive photoreceptor with a peak sensitivity at approximately $530\,nm$.

L-cone

A long-wavelength sensitive photoreceptor with a peak sensitivity at approximately $560\,nm$.

Principle of Univariance

The fact that an individual cone photoreceptor cannot distinguish between changes in light intensity and changes in light frequency, as both affect the cell's firing rate.

Metamers

Physically different spectra of light that result in the same relative cone activation and therefore appear identical to the observer.

Additive colour mixing

The process of combining different light frequencies, such as on a TV screen; adding red, blue, and green light together produces white light.

Subtractive colour mixing

The process of mixing pigments or paints where each addition removes more light; ideally, combining all pigments results in black.

Parvo-path

A pathway consisting of midget ganglion cells (about $80\%$) that has high spatial resolution and distinguishes between $L$ and $M$ cones.

Magno-path

A pathway consisting of parasol ganglion cells (about $10\%$) that is fast, colour blind, and responds well to low contrast by summing $L$ and $M$ cone inputs.

Konio-path

A pathway consisting of bistratified ganglion cells ($8-10\%$) that typically features blue-on and red-green off receptive fields.

Dichromatic Colour Vision

A condition where an organism has only two functional cone types; in humans, this often involves a defective $L$ or $M$ cone, affecting $10\%$ of males and $0.5\%$ of females.

Ishihara colour test plates

Test patterns made of random dots used to diagnose red-green colour deficiency by hiding digits within specific colour variations.

Opponent-Process Theory

The theory that colour perception is determined by two continuously variable channels (red-green and blue-yellow) and a third luminance channel.

Colour Constancy

The ability of the visual system to determine the true colour of an object by normalizing for the composition of the incoming light regardless of changes in illumination.

Midget BP cells

Specific bipolar cells in the retina that connect to exactly one cone each, maintaining high resolution.

Purple

A non-monochromatic colour perception resulting from a mixture of red and blue light, rather than a single wavelength.