PSY2204: Perceptual Processes - Measuring Perception

Sensation and Perception

• Sensation: a physiological process that detects physical energy (e.g., light, sound waves) by sense organs (e.g., eyes, ears), which relay this information to the brain.
• Perception: the selection, organization, and interpretation of sensations, where the brain interprets sensation information to create a meaningful experience.

Muller's Doctrine

• Each sense organ responds to a specific form of energy and translates it into neural firing that the brain can respond to.

Transduction

• The process where sense organs convert energy from environmental events into neural activity through action potentials.

Importance of Perception

• Determines our experience and reaction to the world around us.
• Knowledge can also affect the way we perceive things.

Bottom-up and Top-down Processes

• Sensation: a bottom-up process, transforming energy.
• Perception: a top-down process, interpreting the information.

Studying Perceptual Processes

• Stimulus (distal and proximal; Steps 1-2)
• Physiology (receptors and neural processing; Steps 3-4)
• Behavior (perception, recognition, action; Steps 5-7)

The Stimulus-Behavior Relationship

• Relating stimuli to behavioral responses, such as perception, recognition, and action.
• Examples: psychophysics measures the relationships between the physical stimulus and the behavioral response.

The Stimulus-Physiology Relationship

• Relating stimuli to physiological responses, like neurons firing.
• Examples: measuring brain activity using techniques like optical brain imaging.

The Physiology-Behavior Relationship

• Relating physiological responses to behavioral responses.
• Examples: measuring both brain response and behavioral sensitivity in the same participants.

Psychophysics

• The use of quantitative methods to measure relationships between stimuli (physics) and perception (psycho).
• Quantifying the sensations evoked by physical stimuli.

Components of a Psychophysical Experiment

• Psychophysical stimuli: generated by a computer and presented on a device (e.g., CRT monitor).
• Psychophysical task: the action the observer must perform on each trial (e.g., selecting a stimulus, pressing a button).
• Method: the way the stimuli are presented and the observer's responses are recorded.
• Analysis: how the data are converted into measurements.
• Measure: the result of the analysis (e.g., thresholds, reaction times, proportion correct).

Thresholds

• Detection threshold (Absolute threshold): the smallest detectable stimulus intensity that yields a sensory percept.
• Discrimination threshold (Difference Threshold): the smallest detectable difference between two stimuli that yields a perceptual difference.

Measuring Thresholds

• Method of constant stimuli
• Method of limits
• Method of adjustment (adaptive methods)

Method of Limits

• Presents stimuli in either ascending or descending order.
• Efficient: gets a threshold in a small number of trials.
• Spurious thresholds may be obtained without evidence that the observer was really listening.

Method of Adjustment (Adaptive Methods)

• Subjects adjust stimulus intensity until they can just about detect or discriminate the stimulus.
• Easy and intuitively appealing.
• Produces unreliable results.

Weber's Law

• The just-noticeable difference (JND) is a constant fraction of the stimulus.
• Describes how much of a physical difference is needed between two stimuli before people can just tell the difference.
• Works well except at extremely low or high intensities.

Magnitude Estimation

• The observer assigns numbers to stimuli that are proportional to the perceived magnitude.
• Response compression: as intensity increases, magnitude increases, but not as rapidly.
• Response expansion: as intensity increases, perceptual magnitude increases more than intensity.

Steven's Power Law

• The relationship between the intensity of a stimulus and our perception of its magnitude follows the same general equation for each sense.
• Perceived magnitude, P, equals a constant, K, times the stimulus intensity, S, raised to a power, n.