Dynamic Construction of Reduced Representations in the Brain for Perceptual Decision Behavior

Summary: Over the past decade, extensive studies of the brain regions that support face, object, and scene recognition suggest that these regions have a hierarchically organized architecture that spans the occipital and temporal lobes [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14], where visual categorizations unfold over the first 250 ms of processing [15, 16, 17, 18, 19]. This same architecture is flexibly involved in multiple tasks that require task-specific representations—e.g. categorizing the same object as “a car” or “a Porsche.” While we partly understand where and when these categorizations happen in the occipito-ventral pathway, the next challenge is to unravel how these categorizations happen. That is, how does high-dimensional input collapse in the occipito-ventral pathway to become low dimensional representations that guide behavior? To address this, we investigated what information the brain processes in a visual perception task and visualized the dynamic representation of this information in brain activity. To do so, we developed stimulus information representation (SIR), an information theoretic framework, to tease apart stimulus information that supports behavior from that which does not. We then tracked the dynamic representations of both in magneto-encephalographic (MEG) activity. Using SIR, we demonstrate that a rapid (∼170 ms) reduction of behaviorally irrelevant information occurs in the occipital cortex and that representations of the information that supports distinct behaviors are constructed in the right fusiform gyrus (rFG). Our results thus highlight how SIR can be used to investigate the component processes of the brain by considering interactions between three variables (stimulus information, brain activity, behavior), rather than just two, as is the current norm

Vision: face-centered representations in the brain

A longstanding debate in the face recognition field concerns the format of face representations in the brain. New face research clarifies some of this mystery by revealing a face-centered format in a patient with a left splenium lesion of the corpus callosum who perceives the right side of faces as ‘melted’

Affordances of distractors and compatibility effects: a study with the computational model TRoPICALS

Seeing an object activates in the brain both visual and action codes. Crucial evidence supporting this view is offered by compatibility effect experiments (Ellis et al. (2007). J Exp Psychol: Hum Percept Perform): perception of an object can facilitate or interfere with the execution of an action (e.g. grasping) even when the viewer has no intention of interacting with the object. TRoPICALS (Caligiore et al. (2010). Psychol Rev) is a computational model developed to study compatibility effects. It provides a general hypothesis about the brain mechanisms underlying compatibility effects, suggesting that the top-down bias from prefrontal cortex (PFC), and its agreement or disagreement with the affordances of objects, plays a key role in such phenomena. Compatibility effects have been investigated in the presence of a distractor object in (Ellis et al. (2007). J Exp Psychol: Hum Percept Perform). The reaction times (RTs) results confirmed compatibility effects found in previous experiments without the distractor. Interestingly, results also showed an unexpected effect of the distractor: responding to a target with a grip compatible with the size of the distractor produced slower RTs in comparison to the incompatible case. Here we present an enhanced version of TRoPICALS that reproduces and explains these new results. This explanation is based on the idea according to which PFC might play a double role in its top-down guidance of action selection producing: (a) a positive bias in favor of the action requested by the experimental task; (b) a negative bias directed to inhibiting the action evoked by the distractor. The model also provides two testable predictions on the possible consequences on compatibilities effects of the target and distractor objects in Parkinsonian disease patients with damages of inhibitory circuits

Second order isomorphism: A reinterpretation and its implications in brain and cognitive sciences

Shepard and Chipman's second order isomorphism describes how the brain may represent the relations in the world. However, a common interpretation of the theory can cause difficulties. The problem originates from the static nature of representations. In an alternative interpretation, I propose that we assign an active role to the internal representations and relations. It turns out that a collection of such active units can perform analogical tasks. The new interpretation is supported by the existence of neural circuits that may be implementing such a function. Within this framework, perception, cognition, and motor function can be understood under a unifying principle of analogy

Imaging visually-evoked cortical activity

This work will significantly inform our understanding of \u27neural plasticity\u27, the ability of the brain to respond and reorganize to environmental changes or following an injury or disorder. It is also our hope that the results of this program will inform the design of devices to restore hearing - it might enable tuning of those devices to restore sensory representations in the brain in a patient-specific manner. We believe this will significantly reduce the impact of cognitive disorders that arise as a result of abnormal perception both in children and in older adults.https://ir.lib.uwo.ca/brainscanprojectsummaries/1003/thumbnail.jp

AI: Inventing a new kind of machine.

A means-ends approach to engineering an artificial intelligence machine now suggests that we focus on the differences between human capabilities and the best computer programs. These differences suggest two basic limitations in the "symbolic" approach. First, human memory is much more than a storehouse where structures are put away, indexed, and rotely retrieved. Second, human reasoning involves more than searching, matching, and recombining previously stored descriptions of situations and action plans. Indeed, these hypotheses are related: Remembering and reasoning both involve reconceptualization. This short paper outlines recent work in situated cognition, robotics, and neural networks that suggests we frame the problem if AI in terms of inventing a new kind of machine

A neural network model of visual object recognition impairment after brain damage

Dysfunction of the visual object recognition system in humans is briefly discussed and a basic connectionist model of visual object recognition is introduced. Experimentation in which two variants of this model are lesioned is undertaken. The results suggest that the well documented phenomenon of superordinate preservation is model independent. Differential category specific recognition deficits are also observed in this model, however these are sensitive to each particular variant