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Chapter 5

Chapter 5 Notes - Part two


Department
Psychology
Course Code
PSYA01H3
Professor
Steve Joordens
Chapter
5

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Just noticeable difference
Ernest Weber measured it
Smallest difference between two similar stimuli that can be distinguished; AKA difference
threshold
Weber Fraction: The ratio between a just-noticeable difference and the magnitude of a
stimulus; reasonably constant over the middle range of most stimulus intensities.
Psychophysical methods rely heavily on threshold: the line between not perceiving and
perceiving.
Just-noticeable difference can also be called a difference threshold: the minimum detectable
difference between two stimuli
Absolute threshold: minimum value of a stimulus that can be detected that is,
discriminated from no stimulus at all.
Threshold = not an absolutely fixed value
By convention, it is the point at which a participant detects the stimulus 50% of the time
Signal Detection Theory: Every stimulus event requires discrimination between signal
(stimulus) and noise (consisting of both background stimuli and random activity of the
nervous system)
Response bias: tendency to say yes or no when you are not sure whether you detected the
stimuli
Receiver operating characteristics curve (ROC curve) a graph of hits and false alarms of
participants under different motivational conditions; indicates peoples ability to detect a
particular stimulus
Light consists of radiant energy similar to radio waves
Radiant energy oscillates as it is transmitted from its source
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