Chapter 5 Notes - Part two
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Just noticeable difference
Ernest Weber measured it
Smallest difference between two similar stimuli that can be distinguished; AKA difference
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
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
Response bias: tendency to say ‘yes’ or ‘no’ when you are not sure whether you detected the
Receiver operating characteristics curve (ROC curve) – a graph of hits and false alarms of
participants under different motivational conditions; indicates people’s ability to detect a
Light consists of radiant energy similar to radio waves
Radiant energy oscillates as it is transmitted from its source
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