Effects of nicotine on pupil size and performance during multiple-object tracking in non-nicotine users.

Nicotine has been commonly used in pyschopharmacological studies, showing its benefits as a pharmacological stimulant on cognitive performance. In the current study, we investigated the effects of 2 mg (Experiment 1) and 4 mg (Experiment 2) of nicotine on performance on a multiple-object-tracking task. Participants were young non-smoking adults with no pre-existing attentional deficits. Nicotine and placebo were administered through nicotine and nicotine-free taste-matched chewing gum, respectively. Additionally, we compared pupil size between nicotine and placebo conditions in both experiments. Although we found that pupil size was considerably smaller in the nicotine conditions, nicotine administration did not appear to facilitate behavioural performance. We speculate that nicotine might enhance performance only for certain cognitive functions, and only for specific populations, such as nicotine-deprived smokers.

Hemispheric lateralization in top-down attention during spatial relation processing: a Granger causal model approach.

Magnetoencephalography was recorded during a matching-to-sample plus cueing paradigm, in which participants judged the occurrence of changes in either categorical (CAT) or coordinate (COO) spatial relations. Previously, parietal and frontal lobes were identified as key areas in processing spatial relations and it was shown that each hemisphere was differently involved and modulated by the scope of the attention window (e.g. a large and small cue). In this study, Granger analysis highlighted the patterns of causality among involved brain areas--the direction of information transfer ran from the frontal to the visual cortex in the right hemisphere, whereas it ran in the opposite direction in the left side. Thus, the right frontal area seems to exert top-down influence, supporting the idea that, in this task, top-down signals are selectively related to the right side. Additionally, for CAT change preceded by a small cue, the right frontal gyrus was not involved in the information transfer, indicating a selective specialization of the left hemisphere for this condition. The present findings strengthen the conclusion of the presence of a remarkable hemispheric specialization for spatial relation processing and illustrate the complex interactions between the lateralized parts of the neural network. Moreover, they illustrate how focusing attention over large or small regions of the visual field engages these lateralized networks differently, particularly in the frontal regions of each hemisphere, consistent with the theory that spatial relation judgements require a fronto-parietal network in the left hemisphere for categorical relations and on the right hemisphere for coordinate spatial processing.

Prosopagnosia as a deficit in encoding curved surface.

RP is a case of "developmental" prosopagnosia who, according to brain-imaging segmentation data, shows reduction in volume of a limited set of structures of the right hemisphere. RP is as accurate as control subjects in tasks requiring the perception of nonface objects (e.g., matching subordinate labels to exemplars, naming two-tone images), with the exception of one perceptual task: The matching of different perspectives of amoebae-like stimuli (i.e., volumes made of a single smooth surface). In terms of speed ("efficiency") of responses, RP's performance falls clearly outside the normal limits also in other tasks that include "natural" but nonface stimuli (i.e., animals, artia facts). Specifically, RP is slow in perceptual judgments made at very low (subordinate) levels of semantic categorization and for objects and artifacts whose geometry present much curved features and surface information. We conclude from these analyses that prosopagnosia can be the result of a deficit in the representation of basic geometric volumes made of curved surface. In turn, this points to the importance (necessity) for the normal visual system of such curved and volumetric information in the identification of human faces.

Canonical views of faces and the cerebral hemispheres.

Evidence is given for a special, canonical, status of one specific view in the identification of familiar faces. In the first experiment, subjects identified by name the fully frontal or profile poses of briefly familiarised individuals less efficiently than an intermediate pose. In addition, in a matching experiment using faces seen in different poses, it was found that one specific intermediate pose (corresponding to 22.5 degrees of angle from the full frontal view) was matched more efficiently in the right visual field (RVF) than in the left visual field (LVF). This finding supports the hypothesis of a superiority of the left hemisphere (LH) over the right hemisphere (RH) in processing a familiar face's canonical view. The other tested "noncanonical" views (i.e., full frontal, 45 degrees, and profile) of these same familiar faces were better matched in the LVF (i.e., the RH); especially at low levels of familiarity. We conclude that, for each familiar face, a viewer-centred representation of the canonical (22.5 degrees ) view is stored in the LH's memory system, whereas multiple views of familiar faces are stored in a memory system of the RH. With increasing levels of familiarity other views are increasingly more efficiently encoded by the LH, and in fact for facial self-recognition the full-front view is superior to any of the other tested views. These findings taken together suggest that complementary lateralised memory subsystems in the two cerebral hemispheres store different sets, only partially overlapping, of view-centred face representations.

Identifying objects in conventional and contorted poses: contributions of hemisphere-specific mechanisms.

Three experiments were designed to test the hypothesis that different mechanisms are used to encode objects seen in unfamiliar contortions than are used to encode objects seen in conventional poses. When a familiar non-rigid form (e.g. an animal) is seen in a contorted pose, we hypothesize that object identification may be achieved by (1) encoding the object's parts separately, (2) encoding the spatial relations among the parts, and (3) matching these encoding to a stored structural description. However, once this form has become familiar, its global shape can be directly matched to information stored in memory. Based on the ideal that 'categorical' spatial relations are encoded better by the left cerebral hemisphere and are used in structural descriptions, we predicted a left-hemisphere advantage when one first encodes contorted poses; in contrast, based on the idea that overall shapes are encoded better by the right hemisphere, we predicted a right-hemisphere advantage for encoding the same shapes after they are familiar. Three experiments confirmed these predictions, which supports the hypotheses that different visual mechanisms operate in the recognition of familiar and unfamiliar views of known non-rigid objects. Moreover, correlational analyses between visual-field differences in several perceptual tasks (matching whole pictures to names, body parts to the whole body, and judging categorical spatial relations) revealed that the degree and lateralization of categorical spatial encoding predicts the left hemisphere's initial advantage in the identification of contorted shapes.

Handedness effects on playing a reversed or normal keyboard.

A group of left-handers, approaching the piano for the first time, showed better performance in playing a reversed keyboard (where the pitch decreased from left to right) than a normal keyboard. By testing a separate group of "experienced" left-handers, it was also found that this observed preference that naive left-handers had for the reversed keyboard can disappear with a few years of practice on a normal keyboard. The initial preference for the reversed keyboard shown by left-handers appeared to be specific for this handedness group, as groups of right-handers, regardless of their level of experience with the piano, performed better with the regular keyboard. Finally, based on these results it was hypothesised that left-handers would encounter considerable frustration in learning the "right-handed" piano. However, an informal demographic study of piano students enrolling at a school of music did not reveal a substantially low prevalence of left-handed pianists.

Memory for locations within regions: spatial biases and visual hemifield differences.

Memory for location of a dot inside a circle was investigated with the circle in the center of a computer screen (Experiment 1) or with the circle presented in either the left or the right visual field (Experiment 2). In both experiments, as in Huttenlocher, Hedges, and Duncan's (1991) study, the task was to relocate the dot by marking the remembered location. When errors in angular and radial estimates were considered separately, it was found that, in both experiments, the angular locations of estimates of the dots' positions regressed toward different locations inside each quadrant of the circle; the radial locations of the estimates of dots' positions tended to regress toward locations near the circumference. These variations in the direction of bias appeared to reflect a general shift of estimates toward the upper left arc of the circle. The second experiment replicated the preceding effects but also revealed that the regressions within quadrants of angular values were stronger after right visual field that after left visual field presentations. We interpret the dissociation between visual fields as evidence that memory for categorical spatial relations (Kosslyn, 1987) is more dependent on left-hemisphere than on right-hemisphere processing.

Tactile rod bisection: hemispheric activation and sex differences.

Blindfolded subjects estimated with either hand the center of rods positioned in either left or right hemispace. In one condition, they also performed a concurrent verbal task. Bias and variability of bisection settings were the dependent variables. Bisections performed in left hemispace were biased to the left of true center, more so when the left hand was used. In contrast, bisections performed in right hemispace were biased rightward, more so when the right hand was used. There were no significant differences in variability of bisections in any condition. Interactions of hand with hemispace in which the task was performed differed for the two sexes. Moreover, the secondary verbal task had no effect on either measure. We conclude that of several factors that may underlie bisection biases, attention was the most relevant.

A redrawn Vandenberg and Kuse mental rotations test: different versions and factors that affect performance.

The available versions of the Vandenberg and Kuse (1978) Mental Rotations Test (MRT) have physically deteriorated because only copies of copies are available. We report results from a redrawn version of the MRT and for alternate versions of the test. Males perform better than females, and students drawn from the physical sciences perform better than students drawn from the social sciences and humanities, confirming other reports with the original version of the MRT. Subjects find it very hard to perform the MRT when stimuli require rotation along both the top/bottom axis and the left/right axis. The magnitude of effect sizes for sex (which account, on average, for some 20% of the variance) does not increase with increasing difficulty of the task. Minimal strategy effects were observed and females did not perform differently during the menstrual period as opposed to the days between the menstrual periods. Practice effects are dramatic, confirming other reports with the original MRT, and can also be shown to be powerful in a transfer for practice paradigm, where test and retest involve different versions of the MRT. Main effects of handedness on MRT performance were not found.

Cerebral lateralization for the processing of spatial coordinates and categories in left-and right-handers.

Subjects judged whether a tachistoscopially lateralized drawing was identical or different to a drawing seen immediately before in free vision. The drawings depicted natural objects (e.g. animals). On half of the trials the tachistoscopic drawing presented the same objects but either the categorical or the coordinate spatial relations (according to Kosslyn's definitions [23]) between the objects were transformed. In the first experiment 38 right-handed subjects (half males and half females) were tested. Categorical judgements were faster when the match drawing appeared in the right visual field, whereas coordinate judgements were faster when the match drawing appeared in the left visual field. In the second experiment 26 right-handed and 40 left-handed subjects participated. Almost all the subjects were female. Right-handed subjects replicated the findings of the subjects in the first experiment. However, the LHs did not show any difference in response times between spatial conditions and visual fields. These findings support Kosslyn's hypothesis that the left and right hemispheres are specialized respectively for processing categorical and coordinate spatial relations. Moreover, they also suggest that this lateralization pattern is not typical of left-handers.

Lateralization of categorical and coordinate spatial functions: a study of unilateral stroke patients.

Abstract Sixty patients with unilateral stroke (half with left hemisphere damage and half with right hemisphere damage) and a control group (N = 15) matched for age and educational level were tested in two experiments. In one experiment they were first shown, on each trial, a sample drawing depicting one or more objects. Following a short delay, they were asked to identify the drawing when it was paired with a drawing in which the same object(s) was transformed in categorical or coordinate spatial relations. In the other experiment, the same subjects first were shown, on each trial, a sample drawing. They then judged which of two variants (each in one type of spatial relation) looked more similar to the sample drawing. Typically, patients with left-sided stroke mistakenly identified the categorical transformation for the sample drawing in the first task; in the second task, they judged the categorical transformation as more similar to the sample drawing. Patients with right-sided stroke mistakenly identified the coordinate transformations for the sample drawing in the first task, and, in the second task, typically judged the drawings transformed along coordinate spatial relations as more similar to the sample drawing. These findings provide evidence for complementary lateralization of the two types of spatial perception. It can therefore be inferred that separate functional subsystems process the two types of spatial relations.

Pleasantness of a sweet taste during hunger and satiety: effects of gender and "sweet tooth".

Hungry or sated adult female (N = 29) and male subjects (N = 28), classified according to whether they had eaten or not within 2 h, rated four concentrations of sucrose in a lime drink for their sweetness intensity and pleasantness. Subjects also rated their attitude towards sweets in general (self-reported sweet tooth). Female subjects rated the solutions as less pleasant when tasted soon after a meal. Male subjects showed a non-significant trend in the same direction. Female subjects also rated the solutions as more intense than the male subjects did. Moreover, subjects who reported having a "sweet tooth" (regardless of gender) showed a significant alliesthesia effect (i.e., enhancement of pleasantness of sweet tastes by hunger), whereas those with "no sweet tooth" did not. We conclude that both gender and the degree of individual "sweet tooth" influence alliesthesia.