Adaptable history biases in human perceptual decisions

When making choices under conditions of perceptual uncertainty, past experience can play a vital role. However, it can also lead to biases that worsen decisions. Consistent with previous observations, we found that human choices are influenced by the success or failure of past choices even in a standard two-alternative detection task, where choice history is irrelevant. The typical bias was one that made the subject switch choices after a failure. These choice history biases led to poorer performance and were similar for observers in different countries. They were well captured by a simple logistic regression model that had been previously applied to describe psychophysical performance in mice. Such irrational biases seem at odds with the principles of reinforcement learning, which would predict exquisite adaptability to choice history. We therefore asked whether subjects could adapt their irrational biases following changes in trial order statistics. Adaptability was strong in the direction that confirmed a subject's default biases, but weaker in the opposite direction, so that existing biases could not be eradicated. We conclude that humans can adapt choice history biases, but cannot easily overcome existing biases even if irrational in the current context: adaptation is more sensitive to confirmatory than contradictory statistics

Contradictory Behavioral Biases Result from the Influence of Past Stimuli on Perception

<div><p>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.</p></div

Oscillations of Sensitivity and Response Bias in Auditory Perception

Many behavioural measures of visual perception show continuous rhythmic fluctuations that reflect the influence of neural oscillations in the theta (4-7 Hz) and alpha frequency band (7-12 Hz). This thesis examines whether similar behavioural oscillations exist in audition and if so, how they may be linked to attention and sensory expectation. Three experiments are reported. All employed a similar design that involved the identification of the pitch (Experiment 1) or the ear of origin of a brief, monaural sinusoidal tone masked by uncorrelated broadband noise (Experiment 2 and 3). Experiment 1 confirmed oscillations in auditory sensitivity and revealed, for the first time, rhythmic fluctuations also in response bias. Sensitivity fluctuated at ~6 Hz, while bias exhibited slightly higher frequencies, ~8 Hz. The antiphase characteristic of the sensitivity oscillations between the ears were consistent with spatial attentional sampling. Additional results from Experiment 2 and 3 showed that oscillations in bias at ~9 Hz are related to sensory expectation arising from recent stimulus history. In particular, the oscillations in bias depended on the previous target occurring in the same ear as the current one. This suggests that sensory expectation is communicated through ear- or location-specific reverberations in the alpha band. Additionally, Experiment 3 revealed a new oscillatory effect in auditory behaviour related to unexpected stimulus changes: one trial after an infrequent target occurred, accuracy fluctuated rhythmically at ~7 Hz. These findings highlight the strong influence of oscillatory neural activity on auditory perception. In particular, they show that neural oscillations underlie important aspects necessary to maintain a continuous and coherent percept of the world, by anticipating forthcoming sensory input, sampling the relevant information and updating internal predictions