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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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Performance in trials in which the reference is first (Ref1) and trials in which the reference is second (Ref2) in Reference-Lower protocol (A), and Reference protocol (B).Error bars represent the SEM across the participants. The insets above each bar represent the trial types that constitute that bar using the same notation as in Fig. 1. In Reference-Lower protocol performance is significantly better in Ref2 trials, while in Reference protocol it is better in Ref1 trials.
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pcbi-1003948-g002: Performance in trials in which the reference is first (Ref1) and trials in which the reference is second (Ref2) in Reference-Lower protocol (A), and Reference protocol (B).Error bars represent the SEM across the participants. The insets above each bar represent the trial types that constitute that bar using the same notation as in Fig. 1. In Reference-Lower protocol performance is significantly better in Ref2 trials, while in Reference protocol it is better in Ref1 trials.

Mentions: To examine the interval bias in these two protocols, we divided the trials according to the position of the reference, and measured performance in the two groups of trials separately. As presented in Fig. 2A, in the Reference-Lower protocol, when the reference was in the first interval (Ref1 for short) participants responded correctly in 75.5%±0.7% (mean±SEM across participants) of the trials, compared to 83.9%±0.9% when the reference was in the second interval (Ref2; , paired t-test, , ). Namely, participants performed better when the reference tone was presented in the second interval. When considering the behaviour of each participant individually, 83% of the participants performed better when the reference was presented in the second interval. However, as shown in Fig. 2B, in the Reference protocol, participants responded correctly more often in Ref1 trials (84.4%±0.6%) compared to Ref2 trials (76.2%±0.6%; , paired t-test, , ). Similarly, 73% of the participants performed better in Ref1 trials. When considering only the trials in the Reference protocol in which the frequency of the reference tone was lower than that of the non-reference (i.e., only the trial types that are also present in the Reference-Lower protocol), the results are similar: participants responded correctly more often when the reference was in the first interval (84.6%±0.8%) compared to when the reference was in the second interval (74.0%±1.1%; , paired t-test, , ). The opposite bias in the two experiments refutes the account of better discrimination ability when the reference is presented second, compared to when it is first [2].


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

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

Performance in trials in which the reference is first (Ref1) and trials in which the reference is second (Ref2) in Reference-Lower protocol (A), and Reference protocol (B).Error bars represent the SEM across the participants. The insets above each bar represent the trial types that constitute that bar using the same notation as in Fig. 1. In Reference-Lower protocol performance is significantly better in Ref2 trials, while in Reference protocol it is better in Ref1 trials.
© Copyright Policy
Related In: Results  -  Collection

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

pcbi-1003948-g002: Performance in trials in which the reference is first (Ref1) and trials in which the reference is second (Ref2) in Reference-Lower protocol (A), and Reference protocol (B).Error bars represent the SEM across the participants. The insets above each bar represent the trial types that constitute that bar using the same notation as in Fig. 1. In Reference-Lower protocol performance is significantly better in Ref2 trials, while in Reference protocol it is better in Ref1 trials.
Mentions: To examine the interval bias in these two protocols, we divided the trials according to the position of the reference, and measured performance in the two groups of trials separately. As presented in Fig. 2A, in the Reference-Lower protocol, when the reference was in the first interval (Ref1 for short) participants responded correctly in 75.5%±0.7% (mean±SEM across participants) of the trials, compared to 83.9%±0.9% when the reference was in the second interval (Ref2; , paired t-test, , ). Namely, participants performed better when the reference tone was presented in the second interval. When considering the behaviour of each participant individually, 83% of the participants performed better when the reference was presented in the second interval. However, as shown in Fig. 2B, in the Reference protocol, participants responded correctly more often in Ref1 trials (84.4%±0.6%) compared to Ref2 trials (76.2%±0.6%; , paired t-test, , ). Similarly, 73% of the participants performed better in Ref1 trials. When considering only the trials in the Reference protocol in which the frequency of the reference tone was lower than that of the non-reference (i.e., only the trial types that are also present in the Reference-Lower protocol), the results are similar: participants responded correctly more often when the reference was in the first interval (84.6%±0.8%) compared to when the reference was in the second interval (74.0%±1.1%; , paired t-test, , ). The opposite bias in the two experiments refutes the account of better discrimination ability when the reference is presented second, compared to when it is first [2].

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