Corrigendum
Corrigendum: Signal
Detection Measures Cannot
Distinguish Perceptual Biases
From Response Biases
Perception
2016, Vol. 45(8) 964–965
! The Author(s) 2016
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DOI: 10.1177/0301006616637983
pec.sagepub.com
Owing to errors made by the authors, Jessica K. Witt, J. Eric T. Taylor, Mila Sugovic, and
John T. Wixted, the main conclusion of the article was reached using the wrong formula.
A reevaluation with the correct formula confirmed the main conclusion.
Jessica K. Witt, J. Eric T. Taylor, Mila Sugovic, and John T. Wixted (2015)
Signal Detection Measures Cannot Distinguish Perceptual Biases From
Response Biases Perception, 44, 289–300, doi:10.1068/p7908
The following corrections apply:
The authors simulated data from the Muller-Lyer illusion, which was analyzed using signal
detection theory (SDT) measures d’ and c. The authors misreported the equation for c. The
correct equation, which was used in the analyses (and for the corresponding data plotted in
Figure 1), should be:
c ¼ ½zðhitsÞ þ zðfalse alarmsÞ= 2
ð1Þ
The incorrect equation was used in reporting the values of c in Figure 2, so the authors
recreated Figure 2 below using the correct equation above. The authors have also corrected
the figure caption, which had mislabeled the tails-in versus tails-out conditions
(corrections are bolded in the new figure caption). In addition, the authors have now
posted the R-code for the simulations and the figures at http://amplab.colostate.edu/
MullerLyerSDTsimulations.html. These simulations show that equal shifts due to tail
orientation were modeled for both short and long lines. These corrections do not change
the paper’s main conclusion that, for discrimination experiments, a change in c cannot reveal
whether the bias was perceptual or response-based.
Corrigendum
965
Figure 2. Corrected version of Figure 2 from Witt et al. (2015). The figures represent hypothetical
distributions of perceived line length for short (blue curves) and long (red curves) lines. The vertical purple
line represents the criterion location for classifying a line as long. Panel (a) shows distributions when there is
no perceptual or response-based bias. Panels (b) and (c) show distributions when there are only responsebased biases. Panels (d) and (e) show distributions when there are only perceptual biases. A perceptual bias
towards shorter means that there is a perceptual bias to see the lines as shorter. The left column shows
hypothetical effects on response bias (b) and perceptual bias (d) for the tails-in condition. The right column
shows hypothetical effects on response bias (c) and perceptual bias (e) for the tails-out condition. Note that
both the response bias and the perceptual bias in each column lead to the exact same distribution of hits and
false alarms as each other. For the tails-out condition both types of changes lead to increased hits and false
alarms relative to the baseline condition; for the tails-in condition both types of changes lead to decreased
hits and false alarms relative to the baseline condition. In other words, both types of biases would lead to the
same effect on c. Consequently, an effect in c cannot, in and of itself, differentiate between a perceptual bias
and a response-based bias.