Marc Howard (Boston U.) will give the next Cognitive Bag Lunch presentation at 12pm in Tobin 521B Weds. April 12 at noon. Title and abstract below – all are welcome!

Title: Retrieval of temporal context in the brain is associated with high confidence recognition responses

Abstract: Over the last several decades, models of human episodic memory tasks have bifurcated into models of recall and models of item recognition. Many models of recall have relied heavily on recovery of a gradually-changing state of temporal context. This putative mechanism is sufficient to account for the contiguity effect in recall tasks. In contrast, process models of recognition have focused on accessing traces and matching features. We review recent results from neurobiological data demonstrating that the ensemble response in the brain changes across a wide range of time scales from seconds up to at least several days. We present unpublished results from a study using single unit recordings from an item recognition experiment. Human epilepsy patients studied a list of pictures. The single-unit response changed gradually across stimulus presentations, as predicted by models of temporal context. When an old item was presented as a probe and that probe received a highest confidence response, the neural ensemble “jumped back in time”, recovering the prior state of temporal context. When an old probe did not receive a highest confidence response, the effect was not observed, and in fact showed a weak anti-contiguity effect. We review several unpublished behavioral results and discuss a research strategy for constructing unified models of episodic memory performance that include both recall and recognition results.

The location for the Gallistel talk has been changed to the Cape Cod Lounge of the Student Union Building. Other details are below.

Charles Randy Gallistel, Distinguished Professor Emeritus of Psychology at Rutgers University, will be the 5 Colleges Cognitive Science Speaker this year, in a talk co-sponsored by the Initiative in Cognitive Science. He will present “It’s the neuron! How the brain really works” in the Cape Cod Lounge of the Student Union Building from noon to 1 pm on Wednesday April 19. An abstract and a poster follow.

Abstract. It is generally assumed that the brain’s computational capacities derive mostly from the structure of neural circuits—how it is wired—and from process(es) that rewire circuits in response to experience. The computationally relevant properties ascribed to the neuron itself have not changed in more than a century: It is a leaky integrator with a threshold on its output (Sherrington, 1906). The concepts at the core of molecular biology were undreamed of in Sherrington’s philosophy. They have transformed biological thinking in the last half century. But they play little role in theorizing about how nervous tissue computes. The possibility that the neuron is a full-blown computing machine in its own right, able to store acquired information and to perform complex computations on it, has barely been bruited. I urge us to consider it.

My reasons are: 1) The hypothesis that acquired information is stored in altered synapses is a conceptual dead end. In more than a century, no one has explained even in principle how altered synapses can carry information forward in time in a computationally accessible form. 2) It is easy to suggest several different models for how molecules known to exist inside cells can carry acquired information in a computationally accessible form. 3) The logic gates out of which all computation may be built are known to be implemented at the molecular level inside cells. Implementing memory and computation at the molecular level increases the speed (operations/s), energy efficiency (operations/J) and spatial efficiency (bits/m3) of computation and memory by many orders of magnitude. 5) Recent experimental findings strongly suggest that (at least some) memory resides inside the neuron.

Alexandra Jesse (UMass) will give the next Cognitive Bag Lunch presentation at 12pm in Tobin 521B on Wednesday April 5th at noon. The title and abstract follow. All are welcome!

Learning about speaker idiosyncrasies in visual speech

Seeing a speaker typically improves speech perception, especially in adverse conditions. Audiovisual speech is more robustly recognized than auditory speech, since visual speech assists recognition by contributing information that is redundant and complementary to the information obtained from auditory speech. The realization of phonemes varies, however, across speakers, and listeners are sensitive to this variation in both auditory and visual speech during speech recognition. But listeners are also sensitive to consistency in articulation within a speaker. When an idiosyncratic articulation renders a sound ambiguous, listeners use available disambiguating information, such as lexical knowledge or visual speech information, to adjust the boundaries of their auditory phonetic categories to incorporate the speech sound into the intended category. This facilitates future recognition of the sound. For visual speech to best aid recognition, listeners likewise have to flexibly adjust their visual phonetic categories to speakers. In this talk, I will present work showing how lexical knowledge and auditory speech information can both assist the retuning of visual phonetic categories to speakers, but that at least the latter type of retuning seems to rely on attentional resources. Furthermore, listeners rapidly form identity representations of unfamiliar speakers’ facial motion signatures, which subserve talker recognition but may also aid speech perception.