An improved method for evaluating inverted encoding models

Inverted encoding models have recently become popular as a method for decoding stimuli and investigating neural representations. Here we present a novel modification to inverted encoding models that improves the flexibility and interpretability of stimulus reconstructions, addresses some key issues inherent in the standard inverted encoding model procedure, and provides trial-by-trial stimulus predictions and goodness-of-fit estimates. The standard inverted encoding model approach estimates channel responses (or reconstructions), which are averaged and aligned across trials and then typically evaluated using a metric such as slope, amplitude, etc.). We discuss how this standard procedure can produce spurious results and other interpretation issues. Our modifications are not susceptible to these methodological issues and are further advantageous due to our decoding metric taking into account the choice of population-level tuning functions and employing a prediction error-based metric directly comparable across experiments. Our modifications also allow researchers to obtain trial-by-trial confidence estimates independent of prediction error which can be used to threshold reconstructions and increase statistical power. We validate and demonstrate the improved utility of our modified inverted encoding model procedure across three real fMRI datasets, and additionally offer a Python package for easy implementation of our approach.

Perceptual inference is impaired in individuals with ASD and intact in individuals who have lost the autism diagnosis

Beyond the symptoms which characterize their diagnoses, individuals with autism spectrum disorder (ASD) show enhanced performance in simple perceptual discrimination tasks. Often attributed to superior sensory sensitivities, enhanced performance may also reflect a weaker bias towards previously perceived stimuli. This study probes perceptual inference in a group of individuals who have lost the autism diagnosis (LAD); that is, they were diagnosed with ASD in early childhood but have no current ASD symptoms. Groups of LAD, current ASD, and typically developing (TD) participants completed an auditory discrimination task. Individuals with TD showed a bias towards previously perceived stimuli—a perceptual process called “contraction bias”; that is, their representation of a given tone was contracted towards the preceding trial stimulus in a manner that is Bayesian optimal. Similarly, individuals in the LAD group showed a contraction bias. In contrast, individuals with current ASD showed a weaker contraction bias, suggesting reduced perceptual inferencing. These findings suggest that changes that characterize LAD extend beyond the social and communicative symptoms of ASD, impacting perceptual domains. Measuring perceptual processing earlier in development in ASD will tap the causality between changes in perceptual and symptomatological domains. Further, the characterization of perceptual inference could reveal meaningful individual differences in complex high-level behaviors.

Sensorimotor Synchronization with Higher Metrical Levels in Music Shortens Perceived Time

The aim of the present study was to investigate if the perception of time is affected by actively attending to different metrical levels in musical rhythmic patterns. In an experiment with a repeated-measures design, musicians and nonmusicians were presented with musical rhythmic patterns played at three different tempi. They synchronized with multiple metrical levels (half notes, quarter notes, eighth notes) of these patterns using a finger-tapping paradigm and listened without tapping. After each trial, stimulus duration was judged using a verbal estimation paradigm. Results show that the metrical level participants synchronized with influenced perceived time: actively attending to a higher metrical level (half notes, longer intertap intervals) led to the shortest time estimations, hence time was experienced as passing more quickly. Listening without tapping led to the longest time estimations. The faster the tempo of the patterns, the longer the time estimation. While there were no differences between musicians and nonmusicians, those participants who tapped more consistently and accurately (as analyzed by circular statistics) estimated durations to be shorter. Thus, attending to different metrical levels in music, by deliberately directing attention and motor activity, affects time perception.

Visual word recognition: Evidence for a serial bottleneck in lexical access

Reading is a demanding task, constrained by inherent processing capacity limits. Do those capacity limits allow for multiple words to be recognized in parallel? In a recent study, we measured semantic categorization accuracy for nouns presented in pairs. The words were replaced by post-masks after an interval that was set to each subject’s threshold, such that with focused attention they could categorize one word with ~80% accuracy. When subjects tried to divide attention between both words, their accuracy was so impaired that it supported a serial processing model: on each trial, subjects could categorize one word but had to guess about the other. In the experiments reported here, we investigated how our previous result generalizes across two tasks that require lexical access but vary in the depth of semantic processing (semantic categorization and lexical decision), and across different masking stimuli, word lengths, lexical frequencies and visual field positions. In all cases, the serial processing model was supported by two effects: (1) a sufficiently large accuracy deficit with divided compared to focused attention; and (2) a trial-by-trial stimulus processing tradeoff, meaning that the response to one word was more likely to be correct if the response to the other was incorrect. However, when the task was to detect colored letters, neither of those effects occurred, even though the post-masks limited accuracy in the same way. Altogether, the results are consistent with the hypothesis that visual processing of words is parallel but lexical access is serial.

Visual word recognition: evidence for a serial bottleneck in lexical access

Reading is a demanding task, constrained by inherent processing capacity limits. Do those capacity limits allow for multiple words to be recognized in parallel? In a recent study, we measured semantic categorization accuracy for nouns presented in pairs. The words were replaced by post-masks after an interval that was set to each subject’s threshold, such that with focused attention they could categorize one word with ~80% accuracy. When subjects tried to divide attention between both words, their accuracy was so impaired that it supported a serial processing model: on each trial, subjects could categorize one word but had to guess about the other (White, Palmer & Boynton, 2018). In the experiments reported here, we investigated how our previous result generalizes across two tasks that require lexical access but vary in the depth of semantic processing (semantic categorization and lexical decision), and across different masking stimuli, word lengths, lexical frequencies and visual field positions. In all cases, the serial processing model was supported by two effects: (1) a sufficiently large accuracy deficit with divided compared to focused attention; and (2) a trial-by-trial stimulus processing tradeoff, meaning that the response to one word was more likely to be correct if the response to the other was incorrect. However, when the task was to detect colored letters, neither of those effects occurred, even though the post-masks limited accuracy in the same way. Altogether, the results are consistent with the hypothesis that visual processing of words is parallel but lexical access is serial.

Reactivation of Previous Experiences in a Working Memory Task

Recent experiences influence the processing of new information even when those experiences are irrelevant to the current task. Does this reflect the indirect effects of a passively maintained representation of the previous experience, or is this representation reactivated when a new event occurs? To answer this question, we attempted to decode the orientation of the stimulus on the previous trial from the electroencephalogram on the current trial in a working memory task. Behavioral data confirmed that the previous-trial stimulus orientation influenced the reported orientation on the current trial, even though the previous-trial orientation was now task irrelevant. In two independent experiments, we found that the previous-trial orientation could be decoded from the current-trial electroencephalogram, indicating that the current-trial stimulus reactivated or boosted the representation of the previous-trial orientation. These results suggest that the effects of recent experiences on behavior are driven, in part, by a reactivation of those experiences and not solely by the indirect effects of passive memory traces.

Creating the Punishment Orientation Questionnaire: An Item Response Theory Approach

The purpose of these studies was to examine the principles people engage in when thinking about punishment, using a new measure (the Punishment Orientation Questionnaire [POQ]). Although traditional conceptualizations of punishment divide it into utilitarianism (e.g., deterrence) and retributivism (“eye for an eye”), we argue that a more useful metric of lay attitudes concerns orientation toward or away from punishment. After pilot testing and factor analysis, we used item response theory to assess four scales: prohibitive utilitarianism (limiting punishment based on utility), prohibitive retributivism (aversion to punishing innocent people), permissive utilitarianism (willingness to give strict punishment based on the benefits thereof), and permissive retributivism (desire for just deserts). The POQ showed good predictive validity for capital jury eligibility and sentencing recommendation in response to a death penalty trial stimulus. This study provides a better understanding of how classic punishment philosophies manifest among laypersons and contributes data outside of classical test theory.