Past events

In natural settings, we make decisions based on streams of partial and noisy information. Arguably, we summarize the perceived information into a probabilistic model of the world, which we can exploit to make decisions. This talk will explore such ‘mental models’ in the context of idealized tasks that can be carried out in the laboratory and modeled quantitatively. The starting point of the talk will be a sequential inference task that probes inference in changing environments, in humans. I will describe the task and an experimental finding, namely, that humans make use of fine differences in temporal statistics when making inferences. While our observations agrees qualitatively with an optimal inference model, the data exhibit biases. What is more, human responses, unlike those of the optimal model, are variable, and this behavioral variability is itself modulated during the inference task. In order to uncover the putative algorithmic framework employed by humans, I will go on to examine a family of models that break away from the optimal model in diverse ways. This investigation will suggest a picture in which humans carry out inference using noisy mental representations. More specifically, rather than representing a whole probability function, human subjects may manipulate probabilities using a (possibly modest) number of samples. The approach just outlined illustrates a range of possible computational structures of sub-optimal inference, but it lacks the appeal of a normative framework. If time permits, I will discuss recent ideas on a normative approach to human inference subject to internal ‘costs’ or ‘drives’, which can explain various biases. While different in its formulation, this approach shares conceptual commonalities with the rational inattention theory and other constrained optimization frameworks in cognitive science.

It is established that the brain is capable of large-scale reorganization following sensory deprivation or injury. What is less clear is what are the rules that guide it. In the blind, many visual regions preserve their task specificity despite being recruited for different sensory input; ventral visual areas, for example, become engaged in auditory and tactile object-recognition. However, we are interested in two questions. First, is sensory deprivation necessary for such task-specific reorganization, or can it happen in non-deprived individuals? In this series of experiments, during 9 months we taught Braille, a tactile alphabet, to sighted individuals and observed the resulting changes with structural and functional MRI. (Siuda, Krzywicka, Bola et al, eLife, 2016). Second, we wondered whether task-specific reorganization is unique to the visual cortex, or alternatively, is it a general principle applying to other cortical areas. Here, we enrolled deaf and hearing adults into an fMRI experiment, during which they discriminated between rhythms. In hearing individuals, rhythm processing is performed mostly in the auditory domain. Our prediction was that if task-specific reorganization applies to the human auditory cortex, performing this function visually should recruit the auditory cortex in the deaf (Bola, Zimmerman et al., PNAS, 2017).

Mammalian whiskers and avian rictal bristles come in a variety of shapes and sizes. Indeed, one of the most striking facial features in all mammals (excluding higher primates and humans) is the presence of whiskers. They are deployed in a wide range of tasks and environments. For example, rodents may use their whiskers to guide arboreal locomotion, whilst seals use theirs to track hydrodynamic trails of vortices shed by the fish upon which they prey (Gläser et al, 2010). Certainly, the evolution of the sense of touch is a recognised cornerstone in mammalian evolution, driving brain complexity and behavioural flexibility. While the whisker system is an established model for sensory information processing, advances in measuring whisker behaviours suggests that whisker movements are also useful for measuring aspects of motor control. Many "whisker specialists" including rodents and pinnipeds employ their whiskers by moving them actively, and all mammals (and even some birds) share a similar muscle architecture that drives the movement of the whiskers. Certainly, changes in whisker movements can indicate a loss of motor control and coordination. In this talk I will consider the anatomy and morphology of whiskers, and consider their function in a range of different species. I will suggest how whisker movements may have evolved, and how they are very important for whisker specialists.

The study of perceptual decision-making is key to understanding complex cognitive behavior. Two decades of recordings in primate parietal cortex suggest that neurons in the lateral intraparietal (LIP) cortex integrate sensory evidence from upstream neurons (presumably MT) in favor of making a decision. However, the causal role of LIP in decision-making had not been tested directly. In this talk, I will present recent experiments that tested whether area LIP—which exhibits strong decision-related activity—is causally related to perceptual decision-making. In contrast to the generally accepted model, we found that inactivation in area LIP had no measurable impact on decision-making behavior (despite having exerted effects in a control task). This finding suggests that strong decision-related activity does not guarantee a causal role in decision-making. To better understand the MT-LIP circuit we then applied a Generalized Linear Model (GLM) to simultaneously recorded MT and LIP neurons. We found that much of MT & LIP responses may be interpreted in simple sensorimotor terms, as opposed to appealing to nuanced cognitive phenomena. These results shift our understanding of decision-related activity in the primate brain and motivate new approaches to further dissecting the circuit.