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(Psychology 3340. Research Seminar in Cognition, Brain, and Behavior) |
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Thursdays at 12:00-1:30pm William James Hall 765 Interested parties from outside the Harvard community are welcome to attend. Subscribe to weekly e-mail reminders Questions: Steve Franconeri, francon@wjh Links: Speakers from previous years Social Lunch Psychology Department |
John Assad
Parietal Cortex and the perception of ambiguous apparent motion
We recorded from parietal neurons in monkeys (Macacca mulatta) trained to report the direction of an apparent motion stimulus consisting of regularly spaced columns of dots surrounded by an aperture. Displacing the dots by half their inter-column spacing produced vivid apparent motion that could be perceived in either the preferred or anti-preferred direction for each neuron. Many neurons in the lateral intraparietal area (LIP) responded more strongly on trials in which the animals reported perceiving the neurons' preferred direction, independent of the hand movement used to report their percept. This selectivity was less common in the medial superior temporal area (MST) and virtually absent in the middle temporal area (MT). Variations in activity of LIP and MST neurons just before motion onset were also predictive of the animals' subsequent perceived direction. These data suggest a hierarchy of representation in parietal cortex, whereby neuronal responses become more aligned with subjective perception in higher parietal areas.
Dave Gallo
Metacognitive monitoring of false memories in aging and Alzheimer's disease
People use two decision processes to help avoid false memories: diagnostic and disqualifying monitoring. Disqualifying monitoring involves the use of knowledge that is logically inconsistent with the occurrence of the questionable event. If such knowledge is accessed, then the questionable event can be rejected as having occurred. Diagnostic monitoring involves a comparison between (1) the memorial evidence for the questionable event and (2) expectations about the memorability of such an event, had it occurred. If the former does not conform to the latter, then the questionable event can be rejected as having occurred. I will present data from two different memory tasks: associative recognition and criterial recognition. In the first task, recollection can be used to disqualify a lure from having occurred; in the second task, recollection can be used to diagnose a lure as not having occurred. Aging impaired disqualifying but not diagnostic monitoring. Alzheimer's disease impaired both.
Brad Duchaine
Developmental Prosopagnosia
Dissociations in developmental prosopagnosics provide evidence about the different mechanisms performing visual recognition and the developmental processes that build those mechanisms. Edward, a developmental prosopagnosic, shows severe impairments with facial identity, facial expressions of emotion, and gender discrimination via the face. He performs normally on tasks involving low-level vision, shape perception, visual closure, within-class object discrimination, and facial feature discrimination. He shows no advantage for upright face matching compared to inverted face matching, and he is unable to detect configural changes in sequentially presented faces. As a result, his deficits with faces appear to result from impairments to mechanisms specialized for face-specific holistic processing. The developmental nature of his disorder indicates that different developmental processes produce object processing mechanisms and face-specific mechanisms.
Robert Sekuler
Remembrance of things just seen: Episodic visual recognition memory
I will discuss studies of visual episodic recognition memory, using low-dimensional stimuli (compound sinusoidal gratings) as well as high-dimensional stimuli (synthetic human faces). Also, I'll describe briefly work on cognitive control of memory. All these model-driven explorations demonstrate the value, in studies of memory, of being able to describe and manipulate stimulus materials in a perceptual metric.
Matthew Finkbeiner
The role of polysemy in masked semantic priming within and across languages
A well-known asymmetry exists in the bilingual masked priming literature in which lexical decision is used: namely, masked primes in the dominant language (L1) facilitate decision times on targets in the less dominant language (L2), but not vice versa. In semantic categorization, on the other hand, priming is symmetrical. In Experiments 1-3 we confirm this task difference, finding robust masked L2-L1 translation priming in semantic categorization but not lexical decision. In formulating an account for these findings, we begin with the assumption of a representational asymmetry between L1 and L2 lexico-semantic representations, such that L1 representations are richly populated and L2 representations are not. According to this representational account, L2-L1 priming does not occur in lexical decision because an insufficient proportion of the L1 representation is activated by the L2 prime. In semantic categorization, we argue that the amount of semantic information recruited to generate a decision is restricted by the task category, and that this restriction enhances the effectiveness of the L2 prime. These assumptions were tested in a within-language setting by pairing many-sense words (e.g. "head") with few-sense words (e.g. "skull"). In lexical decision, robust priming was obtained in the many-to-few direction (analogous to L1-L2), but, no priming was obtained in the few-to-many direction (analogous to L2-L1) using the same word pairs. Priming in semantic categorization, on the other hand, was symmetrical. We interpret these findings in terms of the Sense Model as well as other models of bilingual lexical processing.
Kristin Shutts
Looking for Categories in Infancy: Animals, Vehicles, Blobs, and Food
My research program addesses which knowledge domains and what kinds of property young infants represent. In the first part of my talk, I'll present data from 3 experiments with 7-month-olds investigating the role of category membership (e.g. animals, vehicles) and movement type (translatory motion vs. complex motion) in learning about self-propulsion. The second part of my talk will present data from experiments that bear on the question of whether infants selectively generalize property information (color, shape), depending on the domain (animals, food).
Marvin Chun
Neuroimaging Studies of the Dark Side of Visual Attention
Attentional selection of visual events comes with a severe cost: functional blindness to unattended information. We have described the gap in visual awareness for ignored events as the dark side of visual attention (Chun & Marois, 2002). With regard to this, a classic question concerns how unattended, unreportable visual information is processed. Some experiments reveal evidence for early selection, namely effective filtering that blocks perceptual processing of unattended information. Other studies suggest that late selection may occur, based on evidence for perceptual identification of visual information that does not reach awareness. To help resolve the early and late selection debate, I will present neuroimaging data that clarifies when unattended stimuli are identified or not. The critical factor appears to be how attention is engaged: we observed dissociable effects of increasing the perceptual demands of a task in comparison to manipulations that varied working memory load. Thus, there are different forms of attention that have distinguishable effects on how unattended stimuli are processed.
Albert Galaburda
Sound processing and an animal model of developmental dyslexia
Some reports indicate an association between developmental dyslexia and sound processing. We have developed an animal models whereby the brain findings of dyslexia are mimicked and the animal is studied vis à vis sound processing. Thus an causal association is established between brain and sound processing findings in dyslexia, although the whole dyslexia story is likely to be more complex.