Psychophysics• 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 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
• Gestalt Principle– Phi Phenomenon Examples– Illusion of movement
Perception
• Perceptual Constancy– Ability to see things differently without
having to reinterpret the objects properties
– Size– Shape– Brightness