Sensation, Thresholds, and Psychophysics (6A) - MCAT Psychological and Social Foundations

$\frac{\Delta I}{I}=k$. States that JND is a constant proportion of stimulus intensity.

$k=0.05$. Rearrange Weber's law: $k = \frac{\Delta I}{I} = \frac{10}{200} = 0.05$.

Greater sensitivity (smaller proportional change needed to detect a difference). Lower $k$ means smaller changes are detectable, indicating better sensitivity.

Perceived intensity increases logarithmically with stimulus magnitude. Equal increases in stimulus produce smaller increases in perceived intensity.

No signal present but the observer responds "yes". Incorrectly reporting a signal when only noise is present.

Signal present but the observer reports not detecting it. Failing to detect a present signal.

Organization and interpretation of sensory information into meaning. Brain processes that create meaningful experiences from sensory data.

Method of constant stimuli. Plots detection probability across intensities for precise threshold.

Processing of stimuli presented below the absolute threshold. Weak stimuli can influence behavior without conscious awareness.

Reduced response via central processing; adaptation is receptor-level change. Habituation involves higher brain centers, not just receptors.

Decreased sensitivity after prolonged, constant stimulation. Receptors reduce firing to maintain sensitivity range.

No signal present but the observer reports “signal present”. Type I error: detecting signal when only noise exists.

Signal present and the observer reports “signal present”. Correct detection of an actual signal.

Decision threshold for saying “signal present,” influenced by costs and context. Reflects expectations and consequences of errors.

Ability to distinguish signal from noise; higher $d'$ means better detection. Measures true detection ability independent of response bias.

Detection as a function of signal strength, noise, and decision criterion. Separates sensory sensitivity from decision-making factors.

Weber's law. Describes how JND scales with stimulus intensity.

$\Delta I=10$. Apply Weber's law: $\Delta I = k \times I = 0.05 \times 200$.

$\Delta I=4$. Apply Weber's law: $\Delta I = k \times I = 0.10 \times 40$.

Weber fraction; modality-specific constant of proportional sensitivity. Ratio remains constant within each sensory modality.

$\frac{\Delta I}{I}=k$. JND is proportional to baseline intensity, not absolute.

Smallest detectable difference between two stimuli $50%$ of the time. Statistical threshold for discriminating between similar stimuli.

Minimum stimulus intensity detected $50%$ of the time. Statistical threshold where detection probability equals chance.

Conversion of stimulus energy into electrochemical neural signals. Physical stimuli become action potentials via specialized receptors.

Detection and transduction of physical energy into neural signals. Raw sensory input before brain processing creates meaning.

Signal present and the observer reports detecting it. Correct positive response in detection task.

Perception grows slower than intensity (compressive function). Perceived intensity increases slower than actual intensity.

Detection depends on sensitivity and decision criterion under uncertainty. Separates sensory sensitivity from response bias.

Signal absent but the observer reports detecting it. Type I error; detecting signal when none exists.