Basic Concepts in Sensation and Perception

Sensation

The detection of physical energy from the external environment and its encoding into neural signals.

Perception

The psychological process of selecting, organizing, interpreting, and attaching meaning to incoming sensory information.

Distal stimulus

The physical object or event in the external environment that provides energy to sensory systems (e.g., light reflected from an object).

Proximal stimulus

The immediate energy pattern received by specialized sensory receptor cells (e.g., photons striking cells on the retina).

Bottom-up processing

Data-driven perceptual processing that starts with physical sensory input and proceeds toward higher-level interpretation without relying heavily on prior context.

Top-down processing

Conceptually driven perceptual processing guided by prior knowledge, expectations, memories, and context.

Constructive perception (Bruner)

The theoretical view that perceiving involves an active construction that goes beyond raw stimulus input, which can introduce cognitive and social biases into judgment.

Direct perception (Gibson)

The ecological perspective stating that organisms evolve attunements to an ambient optical array containing all information necessary for survival, without requiring cognitive reconstruction.

Law of Prägnanz

The Gestalt principle asserting that sensory reality is organized into the simplest, most stable, and regular form possible.

Law of Proximity

The Gestalt grouping principle stating that visual elements placed close together in space are perceived as belonging to a unified group.

Law of Similarity

The Gestalt principle that visual elements sharing visual characteristics, such as color or shape, are perceived as a cohesive set.

Law of Continuity

The Gestalt principle stating that intersecting lines or paths are perceived as following the smoothest, most continuous direction.

Law of Closure

The Gestalt tendency to automatically bridge gaps and complete missing contours to perceive an intact, whole figure.

Absolute threshold

The minimum level of stimulus intensity needed for an observer to consciously detect a stimulus $50\%$ of the time.

Difference threshold (Just Noticeable Difference)

The minimum physical change in energy required for an observer to detect a difference between two stimuli.

Weber's Law

The psychophysical principle stating that the ratio of the change in stimulus intensity ($\Delta I$) to the original intensity ($I$) remains constant ($K$), expressed as $\frac{\Delta I}{I} = K$.

Sensory adaptation

A reduction in sensory receptor sensitivity following prolonged, uninterrupted exposure to an unchanging stimulus.

Perceptual set

A cognitive predisposition or mental readiness to perceive a stimulus in a particular way based on expectations, context, or experience.

Classical behaviorism (Watson)

The psychological approach asserting that science must restrict itself to observable stimulus-response ($S \rightarrow R$) relations, excluding internal cognitive states.

Unconditioned stimulus (UCS)

An environmental stimulus that naturally, reflexively, and automatically elicits a physiological response without any prior training.

Unconditioned response (UCR)

An innate, automatic physiological reaction elicited directly by an unconditioned stimulus.

Conditioned stimulus (CS)

An originally neutral stimulus that, after repeated pairing with an unconditioned stimulus, acquires the ability to elicit a learned response.

Conditioned response (CR)

A learned behavioral or physiological reaction elicited by a previously neutral cue following conditioning.

Acquisition phase

The period in classical conditioning during which a neutral stimulus is repeatedly paired with an unconditioned stimulus until the response reaches an asymptote.

Extinction (classical conditioning)

The gradual weakening and cessation of a conditioned response when a conditioned stimulus is repeatedly presented without the unconditioned stimulus.

Spontaneous recovery

The reappearance of an extinguished conditioned response following a rest interval, typically occurring at a lower intensity than the initial asymptote.

Stimulus generalization

The tendency for an organism to emit a conditioned response to stimuli that closely resemble the original conditioned stimulus.

Stimulus discrimination

The learned ability of an organism to respond selectively to a specific conditioned stimulus while ignoring similar non-reinforced stimuli.

Law of Effect (Thorndike)

The principle stating that responses followed by favorable consequences become more likely to reoccur, whereas responses followed by unfavorable outcomes become less likely.

Operant conditioning (Skinner)

A learning paradigm in which voluntary behaviors are emitted by an organism and governed by the consequences that follow them, rather than being elicited by pre-existing reflexes.