Introduction

Research Methods

Fall 2010

Tamás Bőhm

What is psychophysics?

• Subdiscipline of experimental psychology• Measuring the relationship between physical

stimuli and their subjective correlates (percepts)• Physical dimensions: light intensity, sound

intensity, sound frequency etc.• Subjective/perceptual dimensions: brightness,

loudness, pitch, etc.• Psychophysics: usually refers to vision• Psychoacoustics: hearing

Why do we need psychophysics?

• Physical dimensions ≠ perceptual dimensions• Light intensity ≠ brightness

http://web.mit.edu/persci/people/adelson/

Why do we need psychophysics?

• Physical dimensions ≠ perceptual dimensions– If you double the intensity of a tone, you won’t hear it

twice as loud! (only 60% louder)– If you change the frequency of a tone, loudness will

also change (loudness depends both on intensity and on frequency)

• Sound intensity ≠ loudness

Why do we need psychophysics?

• Physical dimensions ≠ perceptual dimensions

Some practical uses

• Absolute threshold of hearing

Some practical uses

• Aging and the absolute threshold of hearing

Wikipedia

Some practical uses

• Hearing aids: compensating for audibility loss by measuring individual audibility curves

pure-tone audiometry

Fletcher, 1929

Some practical uses

• Mp3 music coding:1:10 compression by applying results from psychoacoustics– Absolute and

differencethresholds

– Properties ofbinaural hearing(joint stereo)

– Masking effects

Some practical uses

• Military camouflage: detectability of patterns (different shapes and colors) from different viewing distances, under different conditions