© 2001 Dr. Laura Snodgrass, Ph.D. 1

Mental Chronometry

• Measuring the duration of mental events

with reaction time studies

© 2001 Dr. Laura Snodgrass, Ph.D. 2

Donder’s Subtraction Method

• Simple RT - detection task

Choice RT - discrimination task

discrimination

Choice RT - Simple RT = time to discriminate

detectionstimulus response

detectionstimulus response

© 2001 Dr. Laura Snodgrass, Ph.D. 3

Cued RT

• Time required to reach “optimal readiness”

• RT is time to identify stimulus

0

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400

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pre cue 500ms 1500ms

RT

© 2001 Dr. Laura Snodgrass, Ph.D. 4

Probe RT

• Secondary task technique– measure mental effort of primary task by RT to

secondary task– the more mental effort the first task takes the slower

the RT to the secondary

• Examples– picture matching and tone probe– task difficulty and tone (or light) probe

© 2001 Dr. Laura Snodgrass, Ph.D. 5

Semantic Priming

• Speed up response to a stimulus by priming with a related stimulus

• Shows cognitive associations– nurse and doctor– racial and gender biases (stereotypes)

© 2001 Dr. Laura Snodgrass, Ph.D. 6

Methodological Issues

• Irreducible minimum RT– with practice RT declines– 90-100msec in auditory sys is fastest

• Foreperiod - interval between trials– 1-2 sec best for optimal response– variable foreperiod will increase RT

• Anticipation errors– less than 100msec

• Speed-accuracy trade-off– always measure error rate

© 2001 Dr. Laura Snodgrass, Ph.D. 7

Methodological Issues

• Outliers - very long RTs

• 3 strategies– discard– replace– use median not mean

• Choices– discard any RT > 3sd larger than indiv mean– absolute - any RT > 3,000 msec (3 sec)

– Winsorize - replace with next highest– replace with mean for indiv or group