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M C Mozer

Publications and source records attributed to M C Mozer.

8 recordsLinked to original sources
PubMed2001

Localist attractor networks.

Attractor networks, which map an input space to a discrete output space, are useful for pattern completion--cleaning up noisy or missing input features. However, designing a net to have a given set of attractors is notoriously tricky; training procedures are CPU intensive and often produce spurious attractors and ill-conditioned attractor basins. These difficulties occur because each connection in the network participates in the encoding of multiple attractors. We describe an alternative formulation of attractor networks in which the encoding of knowledge is local, not distributed. Although localist attractor networks have similar dynamics to their distributed counterparts, they are much easier to work with and interpret. We propose a statistical formulation of localist attractor net dynamics, which yields a convergence proof and a mathematical interpretation of model parameters. We present simulation experiments that explore the behavior of localist attractor networks, showing that they yield few spurious attractors, and they readily exhibit two desirable properties of psychological and neurobiological models: priming (faster convergence to an attractor if the attractor has been recently visited) and gang effects (in which the presence of an attractor enhances the attractor basins of neighboring attractors).

Animals↗
PubMed2000

Occlusion, symmetry, and object-based attention: reply to Saiki (2000).

J. Saiki (2000) argued that, because the stimuli used by M. Behrmann, R. S. Zemel, and M. C. Mozer (1998) were confounded by symmetry, conclusions about whether amodally completed objects can benefit from object-based attention are unwarranted. Here, the authors examine J. Saiki's claim further and expand on their view of the mechanisms underlying object-based attention, suggesting that perceptual organization is the process whereby features from a single object are selectively attended. In light of this, they claim that heuristics such as symmetry and collinearity play an important role in the facilitation of features from a single object. In support of this claim, they present data from a further experiment using displays that exploit common fate, another grouping heuristic, and show that, under these conditions, the hallmark of object-based attention, a single-object advantage, is obtained for the occluded (amodally completed) shapes.

Adult↗
PubMed2000

Superadditive effects of multiple lesions in a connectionist architecture: implications for the neuropsychology of optic aphasia.

Neuropsychological disorders have traditionally been understood in terms of a focal lesion to a single component of a cognitive architecture. Optic aphasia (OA) defies explanation in this way. In OA, naming of visual stimuli is impaired in the absence of general visual agnosia or anomia. OA has been explained by positing multiple semantic systems or multiple functional pathways to visual naming. M. J. Farah (1990) instead sketched a parsimonious account based on multiple lesions--to pathways mapping visual input to semantic and semantics to naming responses--and the assumption that the effects of the lesions are superadditive. The authors demonstrate superadditive effects of damage in a connectionist architecture and model other phenomena associated with OA. Multiple lesions with superadditivity provide a novel class of explanations for neuropsychological deficits that previously seemed to imply the existence of highly specialized processing components.

Aphasia↗
PubMed1998

Object-based attention and occlusion: evidence from normal participants and a computational model.

One way of perceptually organizing a complex visual scene is to attend selectively to information in a particular physical location. Another way of reducing the complexity in the input is to attend selectively to an individual object in the scene and to process its elements preferentially. This latter, object-based attention process was examined, and the predicted superiority for reporting features from 1 relative to 2 objects was replicated in a series of experiments. This object-based process was robust even under conditions of occlusion, although there were some boundary conditions on its operation. Finally, an account of the data is provided via simulations of the findings in a computational model. The claim is that object-based attention arises from a mechanisms that groups together those features based on internal representations developed over perceptual experience and then preferentially gates these features for later, selective processing.

Adolescent↗
PubMed1989

Types and tokens in visual letter perception.

Five experiments demonstrate that in briefly presented displays, subjects have difficulty distinguishing repeated instances of a letter or digit (multiple tokens of the same type). When subjects were asked to estimate the numerosity of a display, reports were lower for displays containing repeated letters, for example, DDDD, than for displays containing distinct letters, for example, NRVT. This homogeneity effect depends on the common visual form of adjacent letters. A distinct homogeneity effect, one that depends on the repetition of abstract letter identities, was also found: When subjects were asked to report the number of As and Es in a display, performance was poorer on displays containing two instances of a target letter, one appearing in uppercase and the other in lowercase, than on displays containing one of each target letter. This effect must be due to the repetition of identities, because visual form is not repeated in these mixed-case displays. Further experiments showed that this effect was not influenced by the context surrounding the target letters, and that it can be tied to limitations in attentional processing. The results are interpreted in terms of a model in which parallel encoding processes are capable of automatically analyzing information from several regions of the visual field simultaneously, but fail to accurately encode location information. The resulting representation is thus insufficient to distinguish one token from another because two tokens of a given type differ only in location. However, with serial attentional processing multiple tokens can be kept distinct, pointing to yet another limit on the ability to process visual information in parallel.

Attention↗
PubMed1986

Perceptual interactions in two-word displays: familiarity and similarity effects.

Previous studies have demonstrated the existence of perceptual interactions in the processing of two-word displays such as SAND LANE. When postcued to report one of the two words, subjects often make migration errors, in that the report of the specified word includes a letter of the other word (e.g., LAND or SANE instead of SAND). We find that migrations depend on the abstract, structural similarity of the strings, but not on the physical similarity; on whether the strings are words; and on whether the possible migration responses are words. We also rule out an interpretation of migration errors that attributes them to a guessing strategy. Our findings are interpreted in terms of models in which both strings simultaneously access high-level structural knowledge, that is, knowledge about what sequences of letters fit together to form familiar wholes.

Adult↗
PubMed1983

Letter migration in word perception.

These experiments demonstrate that the perception of two distinct words in a briefLy presented display can interact, causing perceptual migrations of letters from one word to the other. For example, when LINE and LACE are presented, subjects might report seeing LICE or LANE instead of LINE. Several properties of the letter migrations were revealed: (a) Migrations are more frequent when the words are separated by smaller physical distances; (b) a majority of the migrations are a result of letters being copied from one word to the other, not from the interchange of letters of the two words; (c) migrations to a word are less frequent when subjects focus attention on that word; and (d) migrations are far more frequent when the words share letters in common. This last result suggests that migrations are not caused by a loss of spatial information at the letter level, that is, by free-floating letters being wrongly combined. Rather, migrations occur because of structural limitations at a high level of the word-recognition process, perhaps during lexical activation. Implications for models of multiple-word perception are discussed.

Attention↗