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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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Demonstration of possible stimuli in different 2AFC protocols.Each sub-figure represents a trial type. The blue bar represents the reference stimulus. The black bar represents the non-reference (comparison) stimulus. The left bar in each trial represents the stimulus in the first interval and the right bar represents the stimulus in the second interval. The ordinates denote the magnitude of the stimuli (frequency, in our experiments). A: a trial in which the reference stimulus is in the first interval, and the non-reference is higher; B: a trial in which the reference stimulus is in the second interval, and the non-reference is higher; C: a trial in which the reference stimulus is in the first interval, and the non-reference is lower; D: a trial in which the reference stimulus is in the second interval, and the non-reference is lower; In the Reference-Lower protocol only configurations A and B are used, while in the Reference protocol all 4 configurations are equally likely.
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pcbi-1003948-g001: Demonstration of possible stimuli in different 2AFC protocols.Each sub-figure represents a trial type. The blue bar represents the reference stimulus. The black bar represents the non-reference (comparison) stimulus. The left bar in each trial represents the stimulus in the first interval and the right bar represents the stimulus in the second interval. The ordinates denote the magnitude of the stimuli (frequency, in our experiments). A: a trial in which the reference stimulus is in the first interval, and the non-reference is higher; B: a trial in which the reference stimulus is in the second interval, and the non-reference is higher; C: a trial in which the reference stimulus is in the first interval, and the non-reference is lower; D: a trial in which the reference stimulus is in the second interval, and the non-reference is lower; In the Reference-Lower protocol only configurations A and B are used, while in the Reference protocol all 4 configurations are equally likely.

Mentions: Standard measures of discrimination ability utilize paradigms, in which a constant reference (also called standard) is presented in one interval and a varying non-reference (or comparison) is presented in the other interval. While the reported JND is, typically, an aggregate measure that ignores the order of the reference and non-reference stimuli, several studies report that performance level can substantially depend on the temporal interval of the reference stimulus, first or second [3]–[7]. This interval bias has been accounted for as reflecting either better discrimination ability when the reference is in a certain interval, or as a bias favoring one of the possible responses [2], [8] (see also below). However, the direction of preference is inconsistent across studies [2]. Some studies reported better performance in trials, in which the reference is presented in the first interval [3], [8]–[12], whereas others reported better performance when the reference stimulus is presented second ([6], [13], [14] - as re-analyzed by [2]. Note that the presentation of [13], [14] in Fig. 1 of [2] uses the interval of the correct response, and not the position of the reference. Since in [13] subjects had to indicate which interval contained the reference, but in [14] subjects had to indicate which interval contained the non-reference, both experiments actually present better performance in trials in which the reference is second). Therefore, the principles underlying this bias remain elusive.


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

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

Demonstration of possible stimuli in different 2AFC protocols.Each sub-figure represents a trial type. The blue bar represents the reference stimulus. The black bar represents the non-reference (comparison) stimulus. The left bar in each trial represents the stimulus in the first interval and the right bar represents the stimulus in the second interval. The ordinates denote the magnitude of the stimuli (frequency, in our experiments). A: a trial in which the reference stimulus is in the first interval, and the non-reference is higher; B: a trial in which the reference stimulus is in the second interval, and the non-reference is higher; C: a trial in which the reference stimulus is in the first interval, and the non-reference is lower; D: a trial in which the reference stimulus is in the second interval, and the non-reference is lower; In the Reference-Lower protocol only configurations A and B are used, while in the Reference protocol all 4 configurations are equally likely.
© Copyright Policy
Related In: Results  -  Collection

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

pcbi-1003948-g001: Demonstration of possible stimuli in different 2AFC protocols.Each sub-figure represents a trial type. The blue bar represents the reference stimulus. The black bar represents the non-reference (comparison) stimulus. The left bar in each trial represents the stimulus in the first interval and the right bar represents the stimulus in the second interval. The ordinates denote the magnitude of the stimuli (frequency, in our experiments). A: a trial in which the reference stimulus is in the first interval, and the non-reference is higher; B: a trial in which the reference stimulus is in the second interval, and the non-reference is higher; C: a trial in which the reference stimulus is in the first interval, and the non-reference is lower; D: a trial in which the reference stimulus is in the second interval, and the non-reference is lower; In the Reference-Lower protocol only configurations A and B are used, while in the Reference protocol all 4 configurations are equally likely.
Mentions: Standard measures of discrimination ability utilize paradigms, in which a constant reference (also called standard) is presented in one interval and a varying non-reference (or comparison) is presented in the other interval. While the reported JND is, typically, an aggregate measure that ignores the order of the reference and non-reference stimuli, several studies report that performance level can substantially depend on the temporal interval of the reference stimulus, first or second [3]–[7]. This interval bias has been accounted for as reflecting either better discrimination ability when the reference is in a certain interval, or as a bias favoring one of the possible responses [2], [8] (see also below). However, the direction of preference is inconsistent across studies [2]. Some studies reported better performance in trials, in which the reference is presented in the first interval [3], [8]–[12], whereas others reported better performance when the reference stimulus is presented second ([6], [13], [14] - as re-analyzed by [2]. Note that the presentation of [13], [14] in Fig. 1 of [2] uses the interval of the correct response, and not the position of the reference. Since in [13] subjects had to indicate which interval contained the reference, but in [14] subjects had to indicate which interval contained the non-reference, both experiments actually present better performance in trials in which the reference is second). Therefore, the principles underlying this bias remain elusive.

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