Perception

Multisensory and multimodal combinations – both for neurons and perception – generally follow one of three mathematical rules: nonlinear summation (usually vector-like), gated amplification, and weighted averaging. Although there are many possible weighted averages, there are two rules that have particular theoretical appeal – Erwin Schrödinger’s (1926) nonlinear weighted average (proposed for binocular psychophysics) and inverse variance-weighted averaging (MLE) which is the most popular Bayesian model used in perceptual theory. Suppressive multisensory and multimodal neurons are the most natural neural loci for weighted averaging. We obtained five sets of suppressive sensory cortical neuron firing rate data: macaque V1 binocular neurons, macaque MSTd visual-vestibular neurons, cat PLLS audiovisual neurons, ferret PPr visual-tactile and ferret AAF audio-tactile neurons. We modeled all five sets of suppressive sensory neurons with the Schrödinger and MLE models. In all five cases and by two criteria, the Schrödinger model outperformed the MLE model, but the two models’ outcomes were well correlated. This elides the problem of extracting and storing variances/reliabilities in early stages of cortical processing, while producing an outcome broadly compatible with Bayesian processes. Schrödinger’s nonlinear means could serve Bayesian ends. Supported by a supplement to Office of Naval Research MURI Award #N00014-20-1-2163.

Children with dyslexia exhibit atypical motion processing, yet the underlying cognitive mechanisms remain debated. While magnocellular differences have been proposed, recent evidence suggests that higher-level processes such as evidence accumulation and decision-making may also play a role. To disentangle these mechanisms, we employed both two-choice and continuous-response random dot motion (RDM) tasks, manipulating motion coherence and direction integration. A total of 42 children with dyslexia and 33 typically developing peers (ages 7–13) completed these tasks, enabling a comprehensive examination of motion perception at multiple levels of analysis. We applied the drift-diffusion model (DDM) to two-choice tasks and the circular diffusion model (CDM) to continuous-response tasks, providing a fine-grained analysis of evidence accumulation and decision processes. Children with dyslexia exhibited a significantly lower drift rate across all tasks, indicating reduced efficiency in extracting sensory evidence from global motion. However, non-decision time remained comparable between groups, suggesting that early sensory encoding differences alone cannot fully account for group differences in performance. These findings support the hypothesis that dyslexia-related motion processing differences extend beyond magnocellular functioning and involve differences in evidence accumulation and decision-making dynamics. By integrating both discrete- and continuous-outcome decision frameworks, our approach provides deeper insight into the nature of motion perception differences, offering a more detailed characterization of motion errors in dyslexia.

We addressed a fundamental question in auditory perception regarding the relative roles of the right and left ears to binaural auditory detection using the tools of systems factorial technology and integrated hazard function ratios as an efficiency metric. Using a double-factorial design, we measured reaction times (RTs) for the detection of one vs. two pure tones (500 and 3020 Hz) at high and low levels, presented across the ears to young adult participants with typical hearing. Participants completed an OR task in which they depressed a ‘yes’ button when one or two tones were present and a ‘no’ button when stimuli were absent. Capacity measures demonstrated limited (but not fixed) capacity for all conditions, indicating that binaural integration was present but not highly efficient. The integrated hazard function ratios between monaural and binaural conditions illustrated that the relative contributions of the right ear versus the left ear varied with RT, with the dominance tending to be the greatest for the RTs longer than the mean RT. Generally, the right ear tended to dominate the binaural percept for all participants regardless of the frequency presented to that ear. Such results support use of integrated hazard function ratios as a dynamic measure of the relative contributions of the two ears in auditory perception.