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.
Highlights
The measurement of perceptual acuity is at the heart of psychophysics
Performance is quantified using a measure known as Just Noticeable Difference (JND; known as Difference Limen, DL, and difference threshold), which denotes the minimal physical difference between two stimuli that is required for attaining a predefined level of performance
Classical Signal Detection Theory applied to psychophysics [1], asserts that if there is no bias in the selection of one interval over the other, the measured JND in the 2AFC design is independent of internal-criteria and is a good method of estimating the limits of the sensory systems
Summary
The measurement of perceptual acuity is at the heart of psychophysics. A widely used method for measuring perceptual acuity is the two-alternative forced-choice (2AFC) design, in which participants are instructed to compare two sequentially presented stimuli that differ physically along a dimension of interest (e.g., pitch, loudness, duration or brightness). Performance is quantified using a measure known as Just Noticeable Difference (JND; known as Difference Limen, DL, and difference threshold), which denotes the minimal physical difference between two stimuli that is required for attaining a predefined level of performance. Classical Signal Detection Theory applied to psychophysics [1], asserts that if there is no bias in the selection of one interval over the other, the measured JND in the 2AFC design is independent of internal-criteria and is a good method of estimating the limits of the sensory systems. Understanding the origins of these biases is important because it can be used as a window for probing the computational principles underlying perceptual processes
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
