Module 1: Introduction to Psychophysics & Light

Distal Stimulus vs. Proximal Stimulus

Distal: Objective physical energy/objects in the external environment.
Proximal: Energy pattern registered directly on sensory receptors (e.g., image on retina).

Representation in Perception

Brain-driven processing that assigns perceptual meaning to the proximal stimulus.

Doctrine of Specific Nerve Energies

Perceptual experience depends on which nerves/brain regions are stimulated, not how they are stimulated (e.g., mechanically pressing the eye stimulates visual cortex, creating light sensation).

Perceptual Sensitivity vs. Acuity

Sensitivity: Ability to detect tiny amounts of energy (weakest detectable stimulus).

Acuity: Ability to distinguish small details/differences between stimuli.

Difference Threshold (JND)

Just-Noticeable Difference: Minimum change in a stimulus required to perceive a difference.

Weber's Law Equation & Formula Breakdown

ΔI / I = K. ΔI is the Just-Noticeable Difference (JND), I is the initial stimulus intensity, and K is the Weber fraction (constant).

What does Weber's Law state about perceiving changes in stimuli?

The amount a stimulus must change to notice a difference (JND) is a constant proportion of the original stimulus level. Larger starting intensities require larger changes to perceive a difference.

Weber's Law Example: You have 10 candles and a Weber fraction of 0.10 (10%). How many candles must be added to perceive a change in brightness?

1 candle. Calculation: 10 candles x 0.10 = 1 candle. (Total candles needed = 11).

Weber's Law Example: You have 50 pennies and a Weber fraction of 0.10 (10%). How many pennies must be added to feel a change in weight?

5 pennies. Calculation: 50 pennies x 0.10 = 5 pennies. (Total pennies needed = 55).

What happens if a stimulus changes by LESS than the Just-Noticeable Difference (JND)?

You will not consciously perceive any change in the stimulus.

Psychophysics Definition & Purpose

The study of the relationship between physical stimuli (material) and psychological sensory experiences (mental).

Three Research Relationships in Perception Study

Stimulus-Perception (Stimulus-Behavior): Relates physical stimuli directly to behavioral responses.

Stimulus-Physiology: Relates physical stimuli to physiological neural responses.

Physiology-Perception (Physiology-Behavior): Relates physiological neural responses to behavioral responses.

4 Key Psychophysical Methods to Measure Perception

Method of Limits: Presenting stimuli in ascending/descending order to find thresholds.

Magnitude Estimation: Assigning numerical values to perceived stimulus intensity.

Reaction Time: Measuring speed of response to a stimulus.

Recognition: Identifying specific stimuli.