A direct comparison of central tendency recall and temporal integration in the successive field iconic memory task

Working memory flips the direction of serial bias through memory-based decision

Reported perception of a new stimulus is either attracted toward or repelled away from task-irrelevant prior stimuli. While prevailing theories propose that the opposing serial biases may stem from distinct stages of information processing, the exact role of working memory (WM) in the serial bias remains unclear despite its consistent involvement in nearly all pertinent studies. Additionally, it is not well understood whether this bias is primarily driven by the biased representation itself or by the decision-making process for the new stimulus. In the present study, we used an orientation delayed estimation paradigm with an attention-demanding intervening task, designed to disrupt the maintenance of stimulus information to investigate the role of WM in serial bias. In the analysis, we scrutinized the trajectory of mouse reports and response time to investigate how the response unfolds over time. Our findings indicate that the serial bias went from repulsive to attractive when WM maintenance was interrupted by the intervening task, and that the associated response trajectories and response time exhibited patterns that cannot be explained by the biased representation alone. These results demonstrate that the task-irrelevant prior stimulus influences the decision for the new stimulus, with the direction of the bias being determined by attentional demand during WM maintenance, thereby placing significant constraints on existing theories on the serial bias effect.

A quantitative model of ensemble perception as summed activation in feature space

Ensemble perception is a process by which we summarize complex scenes. Despite the importance of ensemble perception to everyday cognition, there are few computational models that provide a formal account of this process. Here we develop and test a model in which ensemble representations reflect the global sum of activation signals across all individual items. We leverage this set of minimal assumptions to formally connect a model of memory for individual items to ensembles. We compare our ensemble model against a set of alternative models in five experiments. Our approach uses performance on a visual memory task for individual items to generate zero-free-parameter predictions of interindividual and intraindividual differences in performance on an ensemble continuous-report task. Our top-down modelling approach formally unifies models of memory for individual items and ensembles and opens a venue for building and comparing models of distinct memory processes and representations.

Independent short- and long-term dependencies in perception

Perception is biased by stimulus history. Both long-term effects such as the central-tendency bias (CTB) and short-term effects such as serial dependence (SD) have been described, but research into the two has remained largely separate. The sources of these effects, however, are highly correlated in stimulus statistics, which can result in a misinterpretation of experimental data. We compared CTB and SD in the perception of color and line length. Observers judged the relative hue or length of consecutive stimuli in a delayed-matching task. Two interstimulus intervals were used to investigate whether elapsed time or the number of stimulus occurrences was more important for SD. We estimated biases by fitting psychometric functions to the data split based on the history features, and we also fit generalized linear mixed models with either CTB, SD, or both included as regressors. We found biases to both recent stimulus history and the cumulative average of stimulus values for both color and line length judgments. The strength and pattern of each of the biases depended on whether all sources of bias were included in the analysis. Within the range of interstimulus intervals tested, the number of intervening stimuli was more important than elapsed time for SD. We conclude that both SD and CTB independently affect perceptual judgments, and that one effect is not an artifact caused by the other. Failing to consider both effects in data analysis can give an erroneous picture of the phenomenon under study.

Perceptual history biases in serial ensemble representation

Ensemble perception refers to the visual system's ability to efficiently represent groups of similar objects as a unified percept using their summary statistical information. Most studies focused on extraction of current trial averages, giving little attention to prior experience effects, although a few recent studies found that ensemble mean estimations contract toward previously presented stimuli, with most of these focusing on explicit perceptual averaging of simultaneously presented item ensembles. Yet, the time element is crucial in real dynamic environments, where we encounter ensemble items over time, aggregating information until reaching summary representations. Moreover, statistical information of objects and scenes is learned over time and often implicitly and then used for predictions that shape perception, promoting environmental stability. Therefore, we now focus on temporal aspects of ensemble statistics and test whether prior information, beyond the current trial, biases implicit perceptual decisions. We designed methods to separate current trial biases from those of previously seen trial ensembles. In each trial, six circles of different sizes were presented serially, followed by two test items. Participants were asked to choose which was present in the sequence. Participants unconsciously rely on ensemble statistics, choosing stimuli closer to the ensemble mean. To isolate the influence of earlier trials, the two test items were sometimes equidistant from the current trial mean. Results showed membership judgment biases toward current trial mean, when informative (largest effect). On equidistant trials, judgments were biased toward previously experienced stimulus statistics. Comparison of similar conditions with a shifted stimulus distribution ruled out a bias toward an earlier, presession, prototypical diameter. We conclude that ensemble perception, even for temporally experienced ensembles, is influenced not only by current trial mean but also by means of recently seen ensembles and that these influences are somewhat correlated on a participant-by-participant basis.