Psychophysics Sensations and Perceptions

Psychophysics –Study of how physical stimuli are translated into psychological experiences Sensation –Raw inputs through our senses to our brain Perception –How our brain organizes and makes sense of the inputs

Sensations Most inputs never register…why? –What don’t we notice? Absolute threshold –Point where something becomes noticeable to our senses –If less than this, we do not notice

Sensation Absolute threshold experiments: –hearing testhearing test –Odor test

Sensations Absolute thresholds for 5 senses: –Hearing: the tick of a watch in quiet conditions at 20 feet –Vision: the flame of a single candle at 30 miles distance on a dark night –Smell: one drop of perfume in a 6 room apartment –Taste: one teaspoon of sugar in 2 gallons of water –Touch: the wing of a fly falling on cheek from 1 cm

Sensation Difference Threshold –The minimum stimulus change from a given level that is reliably detectable –Just Noticeable Difference –Proportional Weber’s Law - logarithmic JND = change in I/I –Weight experiment

Sensations Difference Threshold – Weber’s Law –Pitch: 1/333 –Brightness: 1/60 –Lifted weights: 1/50 –Loudness: 1/10 –Pressure on skin: 1/7 –Taste: 1/5 Which of our senses is the most sensitive to change?

Sensation Signal - Detection Theory –Sensory and decision-making processes that determine what info to process and what to filter –Influenced by distraction level (noise) –Criterion – based on expectations and consequences –Ordering pizza at a party

Sensations Sensory Adaptation –The process of becoming less sensitive to unchanging stimulus –Stimuli are still there, we just don’t notice –Restaurant, Clock, Glasses, Old people

Perception Gestalt Principle –Means “unified whole” –Interpret info by grouping to avoid needless repetition Similarity Proximity Continuity Closure

Perception G.P. Similarity –What do you see? –Why doesn’t your brain Compute each individual part?

Perception G.P. Proximity –What do you see?

Perception G.P. Continuity –What do you see?

Perception G.P. Closure –What do you see?

Perception Gestalt Principle –Phi Phenomenon ExamplesExamples –Illusion of movement

Perception Illusions –Muller-Luyer Illusion

Perception Illusion –Reversible

Perception Illusions –Impossible

Perception Perceptual Constancy –Ability to see things differently without having to reinterpret the objects properties –Size –Shape –Brightness

Perception Distance is perceived by: –Monocular cues –Binocular cues

Perception Monocular Cues –Size –Texture –Overlap –Shadowing –Height –Clarity

Perception Binocular cues –Both eyes needed –Convergence –Retinal disparity