Knowledge that Transforms

This study tested for spatial orienting effects, without awareness, to signals presented in the neglected hemifield of 2 hemispatialneglect patients. The experiment adapted a spatial precuing paradigm for measuring the effects of visual attention. Contralesional orienting hastened subsequent target detection at the location of an extinguished precue. These findings validate a claim that orienting can occur independently of overt detection and indicate that location information is registered in the neglected field.

Serial list learning is thought to be beyond the capabilities of infants before the end of their 1st year. In separate experiments with 3- and 6-month-olds, we studied infants' memory for a serial list using a modified serial probe recognition procedure that was originally developed for monkeys and a precuing procedure that was previously used with human adults. Infants were trained with a three-item list. One day later, they were precued with one list member and tested for recognition of another. When the precue specified valid order information, infants of both ages recognized the test item; when the precue specified invalid order information, infants of neither age did. These findings reveal that even very young infants can learn and remember the order of items on a serial list.

The perception of transparency is a remarkable feat of human vision: A single stimulation at the retina is interpreted as arising from two (or more) distinct surfaces, separated in depth, in the same visual direction. This feat is intriguing because physical transparency is neither necessary nor sufficient for phenomenal transparency. Many conditions for phenomenal transparency have been studied, including luminance, chromaticity, stereo depth, apparent motion, and structure from motion. Figural conditions have also been studied, primarily by Gestalt psychologists, resulting in descriptive laws. Here we extend, and make precise, these laws using the genericity principle and the minima rule for part boundaries. We report experiments that support the psychological plausibility of these refinements. The results suggest that the formation of visual objects and their parts is an early process in human vision that can precede the representation of transparency.

The principle of contralateral organization of the visual and motor systems was exploited to investigate contributions of the cerebral hemispheres to the mental representation of prehension in healthy, right-handed human subjects. Graphically rendered dowels were presented to either the left or right visual field in a variety of different orientations, and times to determine whether an underhand or overhand grip would be preferred for engaging these stimuli were measured. Although no actual reaching movements were performed, a significant advantage in grip-selection time was found when information was presented to the cerebral hemisphere contralateral to the designated response hand. Results are consistent with the position that motor imagery recruits neurocognitive mechanisms involved in movement planning. More precisely, these findings indicate that processes within each cerebral hemisphere participate in mentally representing object-oriented actions of the contralateral hand.

In both Pavlovian conditioning and human causal judgment, competition between cues is well known to occur when multiple cues are presented in compound and followed by an outcome. More questionable is the occurrence of competition between outcomes when a single cue is followed by multiple outcomes presented in compound. In the experiment reported here, we demonstrated blocking (a type of stimulus competition) between outcomes. When the cue predicted one outcome, its ability to predict a second outcome that was presented in compound with the first outcome was reduced. The procedure minimized the likelihood that the observed competition between outcomes arose from selective attention. The competition between outcomes that we observed is problematic for contemporary theories of learning.

In the first twin study of the old-old, individuals 80 years old and older, we examined the relationship between general and specific cognitive abilities from a genetic perspective. That is, we examined the extent to which genetic and environmental factors influence major group factors of cognitive abilities, independent of general cognitive ability. As part of the OctoTwin project in Sweden, general and specific cognitive abilities were assessed in 52 monozygotic and 65 same-sex dizygotic twin pairs 80 years old and older using a battery of seven tests that assess verbal, spatial, speed-of-processing, and memory performance. Results suggest that genetic effects associated with general cognitive ability (g) account for the correlation between g and verbal, spatial, and speed-of-processing abilities. No genetic influences were found for these specific cognitive abilities separate from g. In contrast, memory ability appears to be more distinct genetically from g than are other cognitive abilities. Comparison with younger samples suggests that cognitive abilities relating to speed of processing may be genetically dedifferentiated in the old-old.

The impact of education on racial differences in general cognitive ability was assessed using data from the National Longitudinal Survey of Youth. To control for attrition during the educational process, we compared the scores of individuals who ultimately attained the same level of education but who were tested at different points in their educational careers. Multiple regression analyses revealed that education can have a strong positive effect on cognitive ability in both whites and blacks. Whites benefited more from education than blacks during the high school years, but blacks benefited much more than whites from a college education, substantially narrowing the gap between the races. These findings contradict the hypothesis that racial differences in intelligence are relatively immutable, in part because of the diminishing returns from increases in education.

Visual detection of a line target differing in orientation from a background of lines is assumed to occur early in vision and to involve filter mechanisms acting in parallel over the visual field in retinotopic maps (Foster & Ward, 1991; Treisman, 1985; Wolfe, 1994). But retinotopicality does not imply that early vision takes place in a retinal reference frame. This article briefly reviews experiments on this issue and analyzes their implications regarding early visual processing. The review shows that the spatial frame of reference used in visual search for orientation is dynamically determined by various sensory cues to orientation (Marendaz, Stivalet, Barraclough, & Walkowiac, 1993; Stivalet, Marendaz, Barraclough, & Mourareau, 1995). These findings suggest that intersensory integration and perceptual organization are involved at a processing level preceding visual search. This functional viewpoint is discussed in relation to data from neuroscience and psychology (visual search, microgravity).

Targets are identified faster if they appear at the same level (global vs. local) as the target on the previous trial. This effect has been attributed to a controlled attentional process wherein participants attend to the level containing the target on trial n — 1, thus facilitating performance if target level repeats on trial n. An alternative explanation (Lamb & Yund, 1996) is that automatic activation of level-specific neural mechanisms is responsible. The controlled-process hypothesis predicts better performance whenever target level is predictable, because participants can anticipate, and thus attend to, the appropriate level. The automatic-process hypothesis predicts better performance when target level repeats, regardless of target-level predictability. In the present studies, level repetitions facilitated performance regardless of target-level predictability. The data support the automatic-process explanation of level repetition and other attentional effects. The data illustrate how an automatic process can give rise to performance that seems to reflect more cognitive or strategic mechanisms.