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Contradictory behavioral biases result from the influence of past stimuli on perception.

Raviv O, Lieder I, Loewenstein Y, Ahissar M - PLoS Comput. Biol. (2014)

Bottom Line: Here we consider human performance in the 2AFC tone frequency discrimination task, utilizing two standard protocols.Namely, participants perform better when the reference is in a specific interval.The success of this account implies that even simple discriminations reflect a combination of sensory limitations, memory limitations, and the ability to utilize stimuli statistics.

View Article: PubMed Central - PubMed

Affiliation: The Edmond & Lily Safra Center for Brain Sciences, Interdisciplinary Center for Neural Computation, Hebrew University, Jerusalem, Israel.

ABSTRACT
Biases such as the preference of a particular response for no obvious reason, are an integral part of psychophysics. Such biases have been reported in the common two-alternative forced choice (2AFC) experiments, where participants are instructed to compare two consecutively presented stimuli. However, the principles underlying these biases are largely unknown and previous studies have typically used ad-hoc explanations to account for them. Here we consider human performance in the 2AFC tone frequency discrimination task, utilizing two standard protocols. In both protocols, each trial contains a reference stimulus. In one (Reference-Lower protocol), the frequency of the reference stimulus is always lower than that of the comparison stimulus, whereas in the other (Reference protocol), the frequency of the reference stimulus is either lower or higher than that of the comparison stimulus. We find substantial interval biases. Namely, participants perform better when the reference is in a specific interval. Surprisingly, the biases in the two experiments are opposite: performance is better when the reference is in the first interval in the Reference protocol, but is better when the reference is second in the Reference-Lower protocol. This inconsistency refutes previous accounts of the interval bias, and is resolved when experiments statistics is considered. Viewing perception as incorporation of sensory input with prior knowledge accumulated during the experiment accounts for the seemingly contradictory biases both qualitatively and quantitatively. The success of this account implies that even simple discriminations reflect a combination of sensory limitations, memory limitations, and the ability to utilize stimuli statistics.

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A schematic explanation of the Interval Bias as resulting from the effect of history.Using the same notation of Fig. 1. The horizontal dashed line represents M, the memory trace which estimates the value of the mean stimulus in the block. The value of this trace is not the global mean and is expected to vary between trials. The vertical arrow presents the contraction of the first stimulus towards the memory trace. The arrow is red when this contraction impairs performance, since it increases the probability of an incorrect response. The arrow is white when this contraction is beneficial to performance. A–D: exemplar trials from the Reference protocol; A: a Ref1,  trial; B: a Ref1,  trial; C: a Ref2,  trial; D: a Ref2,  trial; E–H: exemplar trials from the Reference-Lower protocol; E: an easy Ref1 trial; F: a difficult Ref1 trial; G: an easy Ref2 trial; H: a difficult Ref2 trial. Overall, in the Reference-Lower protocol performance is expected to be higher in Ref2 trials, and in the Reference protocol performance is expected to be higher in Ref1 trials.
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pcbi-1003948-g005: A schematic explanation of the Interval Bias as resulting from the effect of history.Using the same notation of Fig. 1. The horizontal dashed line represents M, the memory trace which estimates the value of the mean stimulus in the block. The value of this trace is not the global mean and is expected to vary between trials. The vertical arrow presents the contraction of the first stimulus towards the memory trace. The arrow is red when this contraction impairs performance, since it increases the probability of an incorrect response. The arrow is white when this contraction is beneficial to performance. A–D: exemplar trials from the Reference protocol; A: a Ref1, trial; B: a Ref1, trial; C: a Ref2, trial; D: a Ref2, trial; E–H: exemplar trials from the Reference-Lower protocol; E: an easy Ref1 trial; F: a difficult Ref1 trial; G: an easy Ref2 trial; H: a difficult Ref2 trial. Overall, in the Reference-Lower protocol performance is expected to be higher in Ref2 trials, and in the Reference protocol performance is expected to be higher in Ref1 trials.

Mentions: To see why this could be the case, we commence by considering the simpler case of Reference protocol (Fig. 5A–D). In this case, the comparison tone can be either higher or lower than the reference tone, with probability 0.5. Thus, the memory trace, which corresponds to the weighted average of the frequencies of stimuli in past trials, represents a frequency which is similar to the reference tone. As a result, in Ref1 trials, the contraction is towards the correct value of the stimulus (Fig. 5A,B). By contrast, in Ref2 trials, the contraction of the first tone is towards a value similar to the reference. This will effectively decrease the perceived difference between the tones, which is expected to degrade performance relative to Ref1 trials (Fig. 5C and 5D). This reasoning can qualitatively account for the interval bias of Fig. 2B.


Contradictory behavioral biases result from the influence of past stimuli on perception.

Raviv O, Lieder I, Loewenstein Y, Ahissar M - PLoS Comput. Biol. (2014)

A schematic explanation of the Interval Bias as resulting from the effect of history.Using the same notation of Fig. 1. The horizontal dashed line represents M, the memory trace which estimates the value of the mean stimulus in the block. The value of this trace is not the global mean and is expected to vary between trials. The vertical arrow presents the contraction of the first stimulus towards the memory trace. The arrow is red when this contraction impairs performance, since it increases the probability of an incorrect response. The arrow is white when this contraction is beneficial to performance. A–D: exemplar trials from the Reference protocol; A: a Ref1,  trial; B: a Ref1,  trial; C: a Ref2,  trial; D: a Ref2,  trial; E–H: exemplar trials from the Reference-Lower protocol; E: an easy Ref1 trial; F: a difficult Ref1 trial; G: an easy Ref2 trial; H: a difficult Ref2 trial. Overall, in the Reference-Lower protocol performance is expected to be higher in Ref2 trials, and in the Reference protocol performance is expected to be higher in Ref1 trials.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4256013&req=5

pcbi-1003948-g005: A schematic explanation of the Interval Bias as resulting from the effect of history.Using the same notation of Fig. 1. The horizontal dashed line represents M, the memory trace which estimates the value of the mean stimulus in the block. The value of this trace is not the global mean and is expected to vary between trials. The vertical arrow presents the contraction of the first stimulus towards the memory trace. The arrow is red when this contraction impairs performance, since it increases the probability of an incorrect response. The arrow is white when this contraction is beneficial to performance. A–D: exemplar trials from the Reference protocol; A: a Ref1, trial; B: a Ref1, trial; C: a Ref2, trial; D: a Ref2, trial; E–H: exemplar trials from the Reference-Lower protocol; E: an easy Ref1 trial; F: a difficult Ref1 trial; G: an easy Ref2 trial; H: a difficult Ref2 trial. Overall, in the Reference-Lower protocol performance is expected to be higher in Ref2 trials, and in the Reference protocol performance is expected to be higher in Ref1 trials.
Mentions: To see why this could be the case, we commence by considering the simpler case of Reference protocol (Fig. 5A–D). In this case, the comparison tone can be either higher or lower than the reference tone, with probability 0.5. Thus, the memory trace, which corresponds to the weighted average of the frequencies of stimuli in past trials, represents a frequency which is similar to the reference tone. As a result, in Ref1 trials, the contraction is towards the correct value of the stimulus (Fig. 5A,B). By contrast, in Ref2 trials, the contraction of the first tone is towards a value similar to the reference. This will effectively decrease the perceived difference between the tones, which is expected to degrade performance relative to Ref1 trials (Fig. 5C and 5D). This reasoning can qualitatively account for the interval bias of Fig. 2B.

Bottom Line: Here we consider human performance in the 2AFC tone frequency discrimination task, utilizing two standard protocols.Namely, participants perform better when the reference is in a specific interval.The success of this account implies that even simple discriminations reflect a combination of sensory limitations, memory limitations, and the ability to utilize stimuli statistics.

View Article: PubMed Central - PubMed

Affiliation: The Edmond & Lily Safra Center for Brain Sciences, Interdisciplinary Center for Neural Computation, Hebrew University, Jerusalem, Israel.

ABSTRACT
Biases such as the preference of a particular response for no obvious reason, are an integral part of psychophysics. Such biases have been reported in the common two-alternative forced choice (2AFC) experiments, where participants are instructed to compare two consecutively presented stimuli. However, the principles underlying these biases are largely unknown and previous studies have typically used ad-hoc explanations to account for them. Here we consider human performance in the 2AFC tone frequency discrimination task, utilizing two standard protocols. In both protocols, each trial contains a reference stimulus. In one (Reference-Lower protocol), the frequency of the reference stimulus is always lower than that of the comparison stimulus, whereas in the other (Reference protocol), the frequency of the reference stimulus is either lower or higher than that of the comparison stimulus. We find substantial interval biases. Namely, participants perform better when the reference is in a specific interval. Surprisingly, the biases in the two experiments are opposite: performance is better when the reference is in the first interval in the Reference protocol, but is better when the reference is second in the Reference-Lower protocol. This inconsistency refutes previous accounts of the interval bias, and is resolved when experiments statistics is considered. Viewing perception as incorporation of sensory input with prior knowledge accumulated during the experiment accounts for the seemingly contradictory biases both qualitatively and quantitatively. The success of this account implies that even simple discriminations reflect a combination of sensory limitations, memory limitations, and the ability to utilize stimuli statistics.

Show MeSH
Related in: MedlinePlus