Abstract
Whether visual processing in cortex is best modeled as Bayesian inference using a generative model, or a discriminative model, is an important open question (DiCarlo et al. 2021, CCN/GAC). A critical clue to answering this question lies in the functional role of the ubiquitous feedback connections in cortex (Felleman & Van Essen 1991). Inference in a hierarchical generative framework suggests that their role is to communicate top-down expectations (Lee & Mumford 2003). I will present recent behavioral and neurophysiological results that are compatible with this hypothesis; results that are difficult to explain in the context of alternative hypotheses about the role of feedback signals, attention or learning. Our behavioral results in the context of a classic discrimination task strongly suggest that expectations are communicated from decision-related areas to sensory areas on a time scale of 10s to 100s of milliseconds. In the context of classic evidence integration tasks, this feedback leads to a perceptual confirmation bias that is measurable as both a primacy effect (Lange et al. 2021) and overconfidence (Chattoraj et al. 2021). Importantly, the strength of this bias depends on the nature of the sensory inputs in a way that is predicted by approximate hierarchical inference, and that can explain a range of seemingly contradictory findings about the nature of temporal biases. Finally, I will present empirical evidence for a surprising neural signature of feedback-related expectation signals, namely that they induce information-limiting correlations between sensory neurons, again as predicted from approximate hierarchical inference (Lange et al. 2022).