[visionlist] Forced Choice – please educate me

[Erik Blaser]

(Just quickly before we get into the weeds, I think you were just speaking offhandedly, but I think the left/right and landolt C examples are not nAFC, but “identification” tasks. For the motion direction example, you’d need two stimuli in two places (or two intervals) and then ask e.g., “which went left?”. For a landolt 8AFC, you’d need 8 landolts, and ask e.g., “Which one has the gap in the upper left?” I think it’s best to think of the n in nAFC as the number of stimuli, not response choices. This would all be less confusing if nIFC were more common than nAFC!)

best,
Erik



> On Jan 21, 2025, at 9:17 AM, Michael Bach <bach at uni-freiburg.de> wrote:
>
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> Dear Colleagues:
>
> I have the impression that the general understanding of a psychophysical forced-choice paradigm has changed over the decades.
>
> To my understanding, bias/criterion effects can only be effectively mitigated in an nAFC (n-alternative forced choice) design where the alternatives are _equivalent_. Examples: the pattern is on the right/left (balanced, of course), the stimulus was in the first/second interval, or the gap of a Landolt C is in one of 8 directions. “Equivalence” may be challenging to achieve, particularly in the latter case, where the oblique effect may interfere.  Alternatives such as “seen/not seen” or “go/no” are not equivalent and necessitate measures (d’, …) to address bias/criterion.
>
> For me, nAFC implicitly implied equivalent alternatives, but was this ever the case? Whatever, young scientists do not seem to understand it this way.
>
> While this might be just seen as a nomenclature trifle, the real problem arises due to the prevalent “scientific folklore” that a forced-choice paradigm eliminates the effects of bias / criterion change (which, in particular, occur through perceptual learning in longitudinal studies). However, if forced-choice does not employ _equivalent_ alternatives, this assertion is invalid.
>
> I have encountered opinions suggesting that the addition of a “not seen” button constitutes forced choice (yes…, but:) and also eliminates bias…
>
>
> Looking forward to your advice, best, Michael
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> https://michaelbach.de/
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