Perception Final

Attention

The cognitive process of selectively concentrating on some stimuli while ignoring others

Overt Attention

Directing attention by moving the eyes (or head/body) to focus on a stimulus

Covert Attention

Focusing attention on something without moving the eyes (e.g., peripheral attention while looking straight ahead)

Top-Down Attention

Goal-driven, voluntary attention guided by prior knowledge, expectations, or tasks

Bottom-Up Attention

Stimulus-driven attention triggered by salient features (e.g., bright colors, loud sounds)

Visual Salience

Features like color, contrast, motion that pop out automatically

Interests and Goals

Personal relevance or current tasks guide attention

Scene Schema

Knowledge of typical scenes (e.g., looking for a pillow on a bed, not the ceiling)

Task Demands

Specific requirements of a task (e.g., searching for a red car)

Selective Attention

Focusing on one input while filtering out others

Dichotic Listening Task

Participants hear different messages in each ear and repeat one (shadowing); tests selective attention

Broadbent’s Filter Model (Early Selection Theory, 1958)

Attention filters information early based on physical characteristics (e.g., ear of input); unattended info is lost

Cocktail Party Effect

Ability to focus on one conversation in a noisy room but notice your name elsewhere

Late Selection Theory (Deutsch & Deutsch, 1963)

All information is processed for meaning, but only relevant info reaches awareness

Attenuation Theory (Treisman, 1964)

Unattended info is not fully blocked but weakened (attenuated); meaningful info can still break through

Feature Integration Theory (Treisman, 1980)

We perceive objects by combining features (color, shape, etc.) using focused attention; without attention, features may be incorrectly combined (illusory conjunctions)

Dorsal Attention Network

Top-down network (intraparietal sulcus, frontal eye fields) for voluntary, sustained attention

Ventral Attention Network

Bottom-up network (temporoparietal junction, ventral frontal cortex) for detecting salient or unexpected stimuli

Inattentional Blindness

Failing to notice a fully visible but unexpected object because attention is elsewhere (e.g., “invisible gorilla”)

Change Blindness

Difficulty detecting changes between two scenes if attention is not directed to the changing area

Cerebellar Akinetopsia

Inability to perceive motion due to damage to the middle temporal (MT/V5) area or cerebellum

Detecting Things

Motion helps segregate objects from backgrounds

Perceiving Objects

Motion reveals shape and structure (e.g., biological motion)

Perceiving Depth

Motion parallax – Nearby objects move faster across retina than distant ones

Perceiving Events

Event – A segment of time at a specific location perceived as meaningful

Social Perception

Inferring emotions or intentions from movement (e.g., gait, gestures)

Taking Action

Motion guides navigation and interaction (e.g., catching a ball)

Real Motion

Actual physical movement of an object

Apparent Motion

Perception of motion from rapid succession of static images (e.g., flipbook)

Induced Motion

One object’s motion makes another appear to move (e.g., moon moving behind clouds)

Motion Aftereffects

After viewing moving stimulus, a stationary object appears to move opposite direction (e.g., waterfall illusion)

Ecological Approach to Motion Perception (Gibson)

Motion perception is direct from the optic array without internal computation

Optic Array

The structured pattern of light reaching the eye from surfaces in the environment

Local Disturbance in the Optic Array

A moving object creates a local change in the optic flow pattern

Global Optic Flow

Overall radial pattern of motion when observer moves through the environment

Corollary Discharge Theory

Movement perception depends on comparing motor signals and image displacement signals

Corollary Discharge Signal (CDS)

Copy of motor command sent to brain areas that compare actual retinal motion

Motor Signal (MS)

Command sent to eyes/body to move

Image Displacement Signal (IDS)

Movement of image across retina

Motion Perception in the Brain

Processed along the dorsal stream, especially MT and MST areas

Striate Cortex (V1)

Primary visual cortex; detects basic motion orientation

Middle Temporal Area (MT/V5)

Specialized for motion direction and speed

Medial Superior Temporal Area (MST)

Processes complex motion (optic flow, expansion, rotation)

Superior Temporal Sulcus (STS)

Responsible for biological motion perception

Newsome et al. Experiment

Showed MT neurons’ firing rate correlates with motion coherence in random dot displays

Microstimulation

Stimulating MT neurons biases perception of motion direction

The Aperture Problem

When viewing a moving line through a small aperture, direction is ambiguous; solved by integrating local signals in MT

Cerebral Achromatopsia

Loss of color vision due to cortical damage (e.g., V4/V8)

Classify and identify objects

Color helps distinguish objects (e.g., ripe vs. unripe fruit)

Evolutionary advantage

Detecting food, predators, and mates

Cue to emotions

Red = anger, blushing = embarrassment

Hue

Wavelength (e.g., red, blue)

Saturation

Purity (intensity of hue)

Value

Brightness (light to dark)

Subtractive

Mixing pigments (e.g., paint) – absorbs wavelengths

Additive

Mixing lights (e.g., RGB screen) – adds wavelengths

Trichromatic Theory of Color Vision (Young-Helmholtz)

Three cone types (S, M, L) sensitive to short (blue), medium (green), long (red) wavelengths

Opponent-Process Theory of Color (Hering)

Red-green, blue-yellow, black-white opponent channels; explains afterimages

Cue Approach to Depth Perception

Depth is inferred from multiple visual cues (monocular, binocular, oculomotor)

Convergence

Eyes turning inward for near objects

Accommodation

Lens shape changes to focus

Occlusion

Closer object blocks farther

Relative Height

Higher in visual field = farther (for grounded objects)

Familiar/Relative Size

Known size signals distance

Perspective Convergence

Parallel lines meet at horizon

Atmospheric Perspective

Distant objects blurrier/bluer

Texture Gradients

Texture finer/denser in distance

Shadows

Indicate object position and depth

Stereoscopic Depth Perception

Depth from binocular disparity

Binocular Disparity

Slight difference in images between two eyes

Absolute Disparity

Angle relative to fovea for one eye

Relative Disparity

Difference in disparity between two objects

Crossed Disparity

Object nearer than fixation point (crossed eyes)

Uncrossed Disparity

Object farther than fixation point

The Correspondence Problem

Matching corresponding points in left and right eye images to compute disparity

Frontal Eyes

High binocular disparity, better depth but smaller field of view (predators)

Lateral Eyes

Wide field, little disparity (prey)

Müller-Lyer illusion

Arrowheads make lines appear different lengths

Ponzo (railroad) illusion

Converging lines make top object appear larger

Ames Room

Distorted room creates impossible size comparisons

Sound Wave

Periodic compression and rarefaction of air molecules

Pure Tone (Sine Wave)

Single Frequency

Amplitude

Intensity (loudness)

Frequency

Pitch (Hz)

Decibel (dB)

Unit of sound intensity level

Complex Tone

Multiple frequencies combined

Loudness

Perceptual correlate of amplitude

Pitch

Perceptual correlate of frequency

Timbre

Quality that distinguishes two sounds with same loudness/pitch (e.g., piano vs. violin)

Outer Ear

Pinna, ear canal

Middle Ear

Eardrum, ossicles (malleus, incus, stapes)

Inner Ear

Cochlea (hair cells), auditory nerve

Pathway to the brain

Auditory nerve → Cochlear nucleus → Superior olive → Inferior colliculus → Medial geniculate nucleus (thalamus) → Primary auditory cortex (A1)

McGurk effect

Visual speech (e.g., “ga”) combined with auditory “ba” produces perception “da” — shows multimodal integration