PSY 324 Exam 2

Extrastriate cortex

Area outside of the striate cortex (V1).

Where pathway

Identifies an object's location and movement.

What pathway

Identifies what the object is.

Dorsal pathway

Goes to the parietal lobe.

Ventral pathway

Goes to the temporal lobe.

Monkey study on pathways

Monkeys were trained to either reach for food (where task) or identify a specific object (what task); lesions in different brain areas affected only one ability, showing two separate pathways.

IT cortex

Brain region in the ventral stream important for object recognition; damage causes visual agnosia or difficulty recognizing objects.

Receptive fields in IT vs V1

IT receptive fields are larger and respond to complex objects or faces, while V1 receptive fields are small and respond to simple features like edges and lines.

Agnosia

Inability to recognize objects despite normal vision.

Prosopagnosia

Face blindness; inability to recognize familiar faces.

Purpose of middle vision

Intermediate stage of visual processing where the brain organizes basic features into shapes and objects; acts like a 'computer' interpreting visual input.

Structuralism

Perception is built from simple sensations.

Gestaltism

Perception is organized wholes that are more than the sum of their parts.

Limitations of structuralism

It fails to account for how the brain perceives unified objects rather than disconnected parts.

Gestalt rules for grouping

Principles like proximity, similarity, closure, good continuation, and common fate that group elements into single objects.

How camouflage works

Disrupts Gestalt grouping cues, making an object blend with its background.

Perceptual committees

Networks of neurons that vote and interpret sensory input to decide what we perceive.

Ambiguous figure

Image that can be interpreted in more than one way; challenges perceptual committees because both interpretations are valid.

Gestalt rules for figure vs ground

Rules (e.g., symmetry, surroundedness, size) that help determine which parts of an image are seen as the figure and which as the background.

Global superiority effect

The tendency to perceive the whole shape or pattern before the individual parts.

Naïve template theory

Theory that we have stored templates for every object; problematic because it can't explain recognition of objects from new viewpoints.

Structural description theories

Propose we recognize objects by their parts and relationships; problematic because it may not explain how we recognize variations in shape or texture.

Spectrum of light sensed by human vision

Approximately 400-700 nanometers.

Three steps in color perception

Detection (by cones), discrimination (comparing cone outputs), and appearance (assigning color experience).

Three cone types and wavelengths

S-cones (blue, ~420 nm), M-cones (green, ~535 nm), L-cones (red, ~565 nm).

Principle of univariance

A single photoreceptor can't distinguish color because it only signals overall light intensity; solved by comparing multiple cone types.

Trichromatic theory (Young-Helmholtz theory)

Color vision is based on three cone types sensitive to short, medium, and long wavelengths.

Metamer

Two lights with different wavelength compositions that appear identical in color.

Additive color mixing

Mixing lights adds wavelengths (e.g., red + green = yellow).

Subtractive color mixing

Mixing pigments absorbs wavelengths (e.g., blue + yellow paint = green).

Single cone-opponent cells

Compare signals from one type of cone against another; found in LGN.

Double cone-opponent cells

Combine comparisons across different cones in both center and surround; found in V1.

Color space

A 3D representation of colors based on hue, saturation, and brightness.

Hue, saturation, and brightness

Hue = color type; saturation = intensity or purity; brightness = lightness or darkness.

Opponent color theory

Colors are processed in opposing pairs: red-green, blue-yellow, and black-white.

Evidence for opponent colors

Afterimages and color contrast effects.

Color contrast

Surrounding colors affect perceived color (e.g., gray looks bluish next to yellow).

Color assimilation

Adjacent colors blend together, altering perception toward their average.

Color constancy

Perception of color remains stable under different lighting; explains differences in how people see 'the dress.'

Basic color characteristics

Common across languages, single words, and widely recognizable.

Achromatopsia

Loss of color vision from brain damage.

Anomia

Inability to name colors despite being able to perceive them.

Deuteranope

Missing M-cones (green deficiency).

Tritanope

Missing S-cones (blue deficiency).

Protanope

Missing L-cones (red deficiency).