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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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Related in: MedlinePlus

A schematic explanation of the Contraction Bias and its effect on performance.Using the same notation of Fig. 1. The horizontal dashed line representsM, the estimated value of the mean stimulus in the block. The vertical arrow presents the contraction of the first stimulus towards the mean value. The arrow is white when this contraction is beneficial to performance (A), since it increases the probability of a correct response. The arrow is red when this contraction impairs performance (B).
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pcbi-1003948-g004: A schematic explanation of the Contraction Bias and its effect on performance.Using the same notation of Fig. 1. The horizontal dashed line representsM, the estimated value of the mean stimulus in the block. The vertical arrow presents the contraction of the first stimulus towards the mean value. The arrow is white when this contraction is beneficial to performance (A), since it increases the probability of a correct response. The arrow is red when this contraction impairs performance (B).

Mentions: If the memory of the frequency of the first tone contracts towards a prior frequency, the order of the two stimuli within a trial may have a substantial effect on the level of performance. This is illustrated schematically in Fig. 4A and 4B. In this example, the memory trace of previous frequencies (denoted as M in Fig. 4) is higher than the frequencies of the two stimuli. This contraction is expected to improve performance when the frequency of the first tone is higher than that of the second tone (Fig. 4A) and to impair performance when the frequency of the first tone is lower than that of the second tone (Fig. 4B). While the Bayesian framework predicts that in these settings, the memory trace, which represents the prior distribution of stimuli should be almost constant, we found, in a different protocol, in which the two frequencies were drawn from a wide distribution and there was no repeated reference frequency, that the frequencies of the first tones in the most recent trials have a substantial effect on the memory trace [15]. These results motivated us to test whether this contraction bias can account for the seemingly conflicting biases presented in Figs. 2 and 3.


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 Contraction Bias and its effect on performance.Using the same notation of Fig. 1. The horizontal dashed line representsM, the estimated value of the mean stimulus in the block. The vertical arrow presents the contraction of the first stimulus towards the mean value. The arrow is white when this contraction is beneficial to performance (A), since it increases the probability of a correct response. The arrow is red when this contraction impairs performance (B).
© Copyright Policy
Related In: Results  -  Collection

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

pcbi-1003948-g004: A schematic explanation of the Contraction Bias and its effect on performance.Using the same notation of Fig. 1. The horizontal dashed line representsM, the estimated value of the mean stimulus in the block. The vertical arrow presents the contraction of the first stimulus towards the mean value. The arrow is white when this contraction is beneficial to performance (A), since it increases the probability of a correct response. The arrow is red when this contraction impairs performance (B).
Mentions: If the memory of the frequency of the first tone contracts towards a prior frequency, the order of the two stimuli within a trial may have a substantial effect on the level of performance. This is illustrated schematically in Fig. 4A and 4B. In this example, the memory trace of previous frequencies (denoted as M in Fig. 4) is higher than the frequencies of the two stimuli. This contraction is expected to improve performance when the frequency of the first tone is higher than that of the second tone (Fig. 4A) and to impair performance when the frequency of the first tone is lower than that of the second tone (Fig. 4B). While the Bayesian framework predicts that in these settings, the memory trace, which represents the prior distribution of stimuli should be almost constant, we found, in a different protocol, in which the two frequencies were drawn from a wide distribution and there was no repeated reference frequency, that the frequencies of the first tones in the most recent trials have a substantial effect on the memory trace [15]. These results motivated us to test whether this contraction bias can account for the seemingly conflicting biases presented in Figs. 2 and 3.

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