0010 Ch 5 Gaps (2/2)

What is the opponent-process theory, and who proposed it?

Hering (1878/1964): red/green and blue/yellow are opponent pairs processed at the ganglion-cell stage — one ganglion type is excited by L (red) but inhibited by M (green); another is excited by S (blue) but inhibited by combined L+M (yellow)

How do trichromatic and opponent-process theories fit together?

Trichromatic theory describes the cones (first stage); opponent-process describes the ganglion cells (second stage) — both are correct at different stages

What explains the afterimage in opponent-process theory?

Staring at red fatigues red receptors; looking away leaves green receptors relatively fresh, producing a green afterimage

Define hue, saturation, and lightness

Hue: spectral identity (greenness/orangeness), depends on dominant wavelength. Saturation: purity — single-wavelength spectrum colors vs mixed pastels. Lightness: perceived intensity, depends on total light reaching the eye and background contrast

What does the vase/faces reversible figure (Fig. 5.19) show?

The visual system assigns figure vs ground automatically; only one is perceived at a time, and the assignment flips periodically

What does the Dalmatian figure (Fig. 5.20) show?

Once a part (e.g., the head) is detected, the dog is organized automatically and can't be unseen — experience informs figure/ground judgments

Gestalt principle: proximity

Nearby elements are grouped together

Gestalt principle: similarity

Elements are grouped by resemblance in shape, color, or orientation

Gestalt principle: good continuation

Smooth, continuous contours are grouped

Gestalt principle: closure

Gaps are completed — we see whole shapes from fragments

Gestalt principle: illusory contours

Contours, shapes, or depth are seen where none physically exist

Gestalt principle: common fate

Things moving together are grouped

What relational information does each type of object constancy require?

Size constancy needs distance; shape constancy needs viewing angle; color constancy needs comparison with background wavelengths; lightness constancy needs comparison of object vs background reflectance

What is the core computational principle behind object constancy?

The brain computes relative, not absolute, magnitudes of sensory signals

How does the textbook explain the dress photo (white/gold vs black/blue)?

Ambiguous background lighting leads to different relative color judgments — the same sensation produces different perceptions

What is Shepard's tabletop illusion (Fig. 5.24)?

Two identical tabletop shapes look different because of perspective cues — even tracing and overlaying them doesn't override the automatic perceptual assumption

What is special about the fusiform face region's response to upright faces?

It responds most to upright faces (Kanwisher et al., 1998)

For what distances are binocular depth cues most useful?

Relatively close objects

What is the familiar-size monocular cue?

A known object's size plus its retinal image size tells you its distance

How does position relative to the horizon work as a depth cue?

Below the horizon: higher objects are farther; above the horizon: lower objects are farther

What are pictorial depth cues, and who first identified many of them?

Another name for monocular depth cues (they work in 2D images); many were first identified by Leonardo da Vinci

What does the train example show about motion perception?

With eyes moving and head still, a moving train can look stationary while the station appears to move — motion is judged relative to a frame of reference

What is stroboscopic movement?

Slightly different static images in rapid succession produce apparent motion — how movies work

What is the motion aftereffect (waterfall effect), and what causes it?

After staring at a moving stimulus, a stationary scene briefly appears to move in the opposite direction — caused by fatigue/adaptation of direction-specific motion neurons in a secondary visual area, leaving opposing detectors relatively more active