A decision-time account of individual variability in context-dependent orientation estimation

Abstract

Following exposure to an oriented stimulus, the perceived orientation is slightly shifted, a phenomenon termed the tilt aftereffect (TAE). This estimation bias, as well as other context-dependent biases, is speculated to reflect statistical mechanisms of inference that optimize visual processing. Importantly, although measured biases are extremely robust in the population, the magnitude of individual bias can be extremely variable. For example, measuring different individuals may result in TAE magnitudes that differ by a factor of 5. Such findings appear to challenge the accounts of bias in terms of learned statistics: is inference so different across individuals? Here, we found that a strong correlation exists between reaction time and TAE, with slower individuals having much less TAE. In the tilt illusion, the spatial analogue of the TAE, we found a similar, though weaker, correlation. These findings can be explained by a theory predicting that bias, caused by a change in the initial conditions of evidence accumulation (e.g., prior), decreases with decision time (Dekel & Sagi, 2019b). We contend that the context-dependence of visual processing is more homogeneous in the population than was previously thought, with the measured variability of perceptual bias explained, at least in part, by the flexibility of decision-making. Homogeneity in processing might reflect the similarity of the learned statistics. Highlights The tilt aftereffect (TAE) exhibits large individual differences. Reduced TAE magnitudes are found in slower individuals.  Reduced TAE in slower decisions can be explained by the reduced influence of prior. Therefore, individual variability can reflect decision making flexibility..

Isolating objective and subjective filling-in using the Drift Diffusion Model

“…In Zomet et al (2008) the observers are slow (because of age or lack of practice); thus, the criterion effects are much smaller, showing little dependence on RT, if at all. This agrees with our previous results showing that individual differences in TAE can be explained by RT differences (Dekel & Sagi, 2020a). Although additional modeling details remain somewhat speculative, the basic idea used here, of separately considering RT-dependent and RT-independent effects and interpreting them as changes in how evidence is interpreted (the drift rate) and what priors exist before the evidence (the starting point) seems quite robust.…”

“…In Zomet et al (2008) the observers are slow (because of age or lack of practice); thus, we find the criterion effects to be much smaller, showing little or no dependence on RT (Results, P4). This agrees with our previous results showing that individual differences in TAE can be explained by RT differences (Dekel & Sagi, 2020a).…”

“…To explain the small effect of RT on criterion, we considered the simple idea described in Dekel and Sagi (2020a): that individuals with reduced bias can be explained by having slower decision times. Indeed, we found that observers in Zomet et al (2008) had extremely slow RTs, showing, on average, ~1600 ms for Controls, and ~2700 ms for Patients (see the x-axis of Figure 6B).…”

“…P4: The criterion dependence on distance is expected to be larger at faster RTs, thus to be reduced in slower observers (as discussed above, according to DDM, the starting-point dependent bias decreases with RT (Dekel & Sagi, 2020a)). Here we analyze data from a group of observers diagnosed for depression (Zomet et al, 2008), showing slower RTs.…”

Influences of local and global context on local orientation perception

“…response bias, perceptual bias, reference bias; e.g. Garcia‐Perez & Alcala‐Quintana, 2013; Morgan et al, 2013), we concur and are in line with the opinion of part of the researchers that, since one can self‐experience the perceptual illusion of tilt, the main measure obtained with our design is one of sensory nature, that is, a perceptual bias (Dekel & Sagi, 2020). Therefore, we consider the midpoint of the psychometric function as ‘the perceived (vertical) orientation of the target’ for a given configuration.…”