T-Junction

(See Junctions).

Tapetum

Silvery lining behind the retina in some animals active in dim light. Reflects light back through the eye and allows the photoreceptors a second chance to absorb photons.

Table Illusion

Although the parallelograms making up the top of the two coffee tables are exactly the same size (try checking with a cut out piece of paper) they look different presumably due to our experience with perspective.

Tectopontine Tract

Relays information from the colliculus to the cerebellum for further coordination of eye and head movement.

Tectospinal Tract

Axons from the colliculus to the upper spinal cord where the neck motor neurons are located. Involved in reflex control of head and neck movements.

Template Matching

An object recognition method. Incoming patterns are matched against a set of templates. If there is sufficient overlap between object and template, a match is signaled. Of limited use, primarily in alphanumeric character recognition.

Temporal Hemiretina

That portion of the retina that lies lateral to the fovea. (See also Nasal Hemiretina and Figure).

Terminators

In the context of motion, terminators are those portions of a moving object which signal unambiguous motion. For a barber pole pattern these would be the line ends of the grating, for a translating diamond, these would be the corners.

(See also Aperture Problem)

Extrinsic Terminators

Those terminators that are not created by the end of the object itself. Rather they are due to occlusion by another surface. Such terminators play less of a role in determining the perceived direction of motion than do intrinsic terminators

Intrinsic Terminators

Those terminators that are due to the natural end of the object rather than to occlusion by another surface.

Tetrachromatic Color Vision

Color vision based on four cone photoreceptor pigments in the retina. The fourth cone type is sensitive to U.V. light and seen in goldfish.

(See also Dichromatic Color Vision and Trichromatic Color Vision).

Texton

(Julesz)

The basic textural elements of pre-attentive vision such as elongated blobs or line segments and their terminators which are important for segregation of textures

Texture Segregation

Thick Stripes

(See Appendix I: Cortical Areas, V2).

Thin Stripes

(See Appendix I: Cortical Areas, V2).

Transducin

A regulatory g-protein in photoreceptors which stimulates phosphodiesterase molecules and acts as an amplifier of the incoming light signal.

Transformational Apparent Motion

Apparent motion in which the presented object(s) appear to change shape, growing or contracting. In the simplest case, the line motion illusion, a line that is presented rapidly after a spot appears to smoothy grow out of the spot. There are many variations of this phenomenon. (See also Apparent Motion).

Transient Tritanopia Phenomenon

Transient blindness for blue test lights is observed in the first few hundred milliseconds after the offset of strong yellow adaptations lights.

Trichromatic Color Vision

Color vision based on three cone photoreceptors pigments in the retina

(See also Dichromatic Color Vision and Tetrachromatic Color Vision).

Troland

The unit of retinal illuminance defined as T=Lp with L (luminance) expressed in and p (pupil area) in mm2. Needed as luminance of the light incident on the retina varies with pupil size. There is a photopic and scotopic troland.