Knowledge that Transforms

We examined the cortical representation of semantic categorization using magnetic source imaging in a task that revealed both dissociations among superordinate categories and associations among different base-level concepts within these categories. Around 200 ms after stimulus onset, the spatiotemporal correlation of brain activity elicited by base-level concepts was greater within than across superordinate categories in the right temporal lobe. Unsupervised clustering of data showed similar categorization between 210 and 450 ms mainly in the left hemisphere. This pattern suggests that well-defined semantic categories are represented in spatially distinct, macroscopically separable neural networks, independent of physical stimulus properties. In contrast, a broader, task-required categorization (natural/man-made) was not evident in our data. The perceptual dynamics of the categorization process is initially evident in the extrastriate areas of the right hemisphere; this activation is followed by higher-level activity along the ventral processing stream, implicating primarily the left temporal lobe.

Does perceptual grouping operate early or late in visual processing? One position is that the elements in perceptual layouts are grouped early in vision, by properties of the retinal image, before perceptual constancies have been determined. A second position is that perceptual grouping operates on a postconstancy representation, one that is available only after stereoscopic depth perception, lightness constancy, and amodal completion have occurred. The present experiments indicate that grouping can operate on both a preconstancy representation and a postconstancy representation. Perceptual grouping was based on retinal color similarity at short exposure durations and based on surface color similarity at long durations. These results permit an integration of the preconstancy and postconstancy positions with regard to grouping by color.

We describe a new method for mapping spatial attention that reveals a pooling of attention in the hemifield opposite a peripheral flash. Our method exploits the fact that a brief full-field blank can interfere with the detection of changes in a scene that occur during the blank. Attending to the location of a change, however, can overcome this change blindness, so that changes are detected. The likelihood of detecting a new element in a scene therefore provides a measure of the occurrence of attention at that element's location. Using this measure, we mapped how attention changes in response to a task-irrelevant peripheral cue. Under conditions of visual fixation, change detection was above chance across the entire visual area tested. In addition, a "hot spot" of attention (corresponding to near-perfect change detection) elongated along the cue-fixation axis, such that performance improved not only at the cued location but also in the opposite hemifield.

We investigated the phenomenon of limb-specific locomotor adaptation in order to adjudicate between sensory-cue-conflict theory and motor-adaptation theory. The results were consistent with cue-conflict theory in demonstrating that two different leg-specific hopping aftereffects are modulated by the presence of conflicting estimates of self-motion from visual and nonvisual sources. Experiment 1 shows that leg-specific increases in forward drift during attempts to hop in place on one leg while blindfolded vary according to the relationship between visual information and motor activity during an adaptation to outdoor forward hopping. Experiment 2 shows that leg-specific changes in performance on a blindfolded hopping-to-target task are similarly modulated by the presence of cue conflict during adaptation to hopping on a treadmill. Experiment 3 shows that leg-specific aftereffects from hopping additionally produce inadvertent turning during running in place while blindfolded. The results of these experiments suggest that these leg-specific locomotor aftereffects are produced by sensory-cue conflict rather than simple motor adaptation.

Antigravity hills, also known as spook hills or magnetic hills, are natural places where cars put into neutral are seen to move uphill on a slightly sloping road, apparently defying the law of gravity. We show that these effects, popularly attributed to gravitational anomalies, are in fact visual illusions. We re-created all the known types of antigravity spots in our laboratory using tabletop models; the number of visible stretches of road, their slant, and the height of the visible horizon were systematically varied in four experiments. We conclude that antigravity-hill effects follow from a misperception of the eye level relative to gravity, caused by the presence of either contextual inclines or a false horizon line.

This article explores expertise in tactile object recognition. In one study, participants were trained to differing degrees of accuracy on tactile identification of two-dimensional patterns. Recognition of these patterns, of inverted versions of these patterns, and of subparts of these patterns was then tested. The inversion effect (better recognition of upright than inverted patterns) and the part-whole effect (better recognition of the whole than a part pattern), traditionally considered signatures of visual expertise, were observed for tactile experts but not for novices. In a second study, participants were trained as visual or tactile experts and then tested in the trained and nontrained modalities. Whereas expertise effects were observed in the modality of training, cross-modal transfer was asymmetric; visual experts showed generalization to haptic recognition, but tactile experts did not show generalization to visual recognition. Tactile expertise is not obviously attributable to visual mediation and emerges from domain-general principles that operate independently of modality.

Learning in stochastic environments is increasingly viewed as an important psychological ability. To extend these results from a perceptual to a motor domain, we tested whether participants could learn to solve a stochastic minimal-time task using exploratory learning. The task involved moving a cursor on a computer screen to a target. We systematically varied the degree of random error in movement in three different conditions; each condition had a distinct time-optimal solution. We found that participants approximated the optimal solutions with practice. The results show that adults are sensitive to the stochastic structure of a task and naturally adjust the magnitude of an undershoot bias to the particular movement error of a task.

Family characteristics influence children's behavioral development, but so do variations in schools, neighborhoods, and communities. We documented extrafamilial environmental effects by fitting maximum likelihood models to questionnaire data collected from double dyads consisting of twins and their classmate controls. The classmate controls in each double dyad were genetic strangers living in separate households, but they shared school, neighborhood, and community environments with their yoked twin pair and with one another. At ages 11 to 12, the control classmates showed significant similarities in religious practices and smoking and drinking patterns, demonstrating that environmental influences outside the family affect children's behavioral development. Familial self-selection of residential neighborhoods may have contributed to these results, but direct effects of variation across communities, neighborhoods, and schools cannot be dismissed, and such effects warrant further study.

This article presents a theory of how individuals detect whether descriptions of an entity are consistent or inconsistent. The theory postulates that individuals try to construct a mental model of the entity in which all the propositions are true. If they succeed, they infer that the description is consistent; otherwise, they infer that it is inconsistent. We report three experiments that corroborated the theory. Experiment 1 confirmed that evaluating consistency is easier when an initial model suffices than when reasoners have to find an alternative model. Experiment 2 established the occurrence of illusion, inferences about the properties of entities. Experiment 3 showed that the illusions correspond to mental models of the assertions, even when these models are wrong because they fail to represent what is false.

We examined the extent to which young Hong Kong Chinese children, taught to read English as a second language via a logographic "look and say" method used information about letter names and letter sounds to learn English words. Forty children from each of three kindergarten grade levels (mean ages 3.8, 5.0, and 5.9 years old, respectively) were taught to pronounce novel English spellings that were based on letter-name (e.g., DK = Deke), letter-sound (DK = Dick), or visual (DK = Jean) cues. By the 2nd year of kindergarten, children performed significantly better in the name condition than the other conditions. The 3rd-year kindergartners performed better in the sound condition than the visual condition as well. The results point to the importance of letter-name and letter-sound knowledge for learning to read English, regardless of native-language background or method of instruction.