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Simple vs. Complex decisions

Simple decisions involve single attributes (e.g., stop/go at a light); complex decisions involve multiple attributes and long deliberation (e.g., buying a phone).

Two primary sources of information about decision processes

Choice probabilities (accuracy) and decision time (Response Time/RT).

Speed-Accuracy Tradeoff (SATO)

The phenomenon where one can be fast at the expense of accuracy, or accurate at the expense of speed; it shows that accuracy and RT are intimately related.

Psychophysics

The 19th-century discipline studying the relationship between the physical properties of stimuli and their psychological/sensory effects.

Empiricism

The philosophical idea that all knowledge of the world comes through our senses (e.g., John Locke’s "blank tablet").

Just Noticeable Difference (JND)

The smallest difference on a stimulus dimension that can just be distinguished from a comparison stimulus.

Weber’s Law

The principle that the JND is a constant fraction of the comparison stimulus.

Weber Fraction

The constant ratio () for a specific sensory modality; for example, 0.043 for lifted weights or 0.302 for taste/caffeine.

Fechner’s Law

The claim that sensation is a logarithmic function of stimulus intensity ().

Extensive Measurement

A measurement scale constructed by taking identical units and laying them end-to-end (concatenation).

Why Fechner believed sensation is logarithmic

Because the log function is the only function that converts equal multiplicative changes in stimulus strength into equal additive changes in sensation.

Threshold (Limen)

The minimum intensity needed to detect a stimulus; historically thought to be a point of discontinuity.

Empirical Psychometric Function

A smooth, S-shaped sigmoid curve showing detection probability against stimulus intensity, with no evidence of a sudden step-function threshold.

Neural Noise

Random, background neural activity that causes stimulus encoding to vary from trial to trial, resulting in probabilistic performance.

Central Limit Theorem (re

Neural Noise)

Phi-Gamma Hypothesis

The claim that the psychometric function is a cumulative normal distribution, reflecting the increasing proportion of sensory effect distributions falling above a threshold.

Precision (h)

The steepness of the psychometric function, which reflects the amount of noise in the nervous system.

Thurstone’s Law of Comparative Judgment

A model applying psychophysical theory to discrimination (finding a JND) by comparing two noisy internal representations.

Thurstone’s Scaling of Seriousness of Crimes (1927)

A landmark study showing psychophysical methods could scale abstract social values on a single underlying axis; it is the basis of modern scaling theory.

Point of Subjective Equality (PSE)

The crossover point in discrimination judgments where stimulus B is judged equal to stimulus A.

Major limitation of Classical Psychophysics

It cannot explain why experimental instructions (lax vs. strict) move the psychometric function along the axis, which necessitates a theory of response bias.