Which factors affect hand selection in children's grasping in hemispace? Combined effects of task demand and motor dominance

Sixty-five right- and left-handed preschool and school children were tested on three reach-to-grasp tasks of different levels of complexity, performed in three space locations. Our goal was to evaluate how the effect of attentional information related to object location interacts with task complexity and degree of handedness on children's hand selection. Results revealed a shift to the non-preferred hand in the contralateral hemispace, which was more or less pronounced according to the level of task complexity. The subject's degree of handedness also influenced this shift, since strongly lateralized children exhibited a greater use of their preferred hand than less lateralized ones for actions in the contralateral hemispace. These findings confirm that hand selection is to some extent adaptable to task demand and environmental context.     

Are variations among subjects in lateral asymmetry real individual differences or random error in measurement? Putting variability in its place

The current research investigates sources of variability in subjects' asymmetry scores on commonly used laterality tasks. In particular, subjects' asymmetry scores on four bilateral tachistoscopic tasks and one free-vision task were entered into a principal component analysis (PCA) in order to investigate components that explain the maximum variance of the sample. The results indicate that about half of the variation (45.2%) in asymmetry scores on both tachistoscopic and free-vision tasks is attributable to individual differences in characteristic perceptual asymmetry. The amount of variance explained by this characteristic perceptual asymmetry component is similar in a sample of dextrals and a sample of sinistrals. No significant relation was revealed between individual differences in characteristic perceptual asymmetry and performance on various verbal and spatial cognitive tasks.     

Bodily self and schizophrenia: The loss of implicit self-body knowledge

Schizophrenia spectrum has been associated with a disruption of the basic sense of self, which pertains, among others, the representation of one's own body. We investigated the impact of either implicit or explicit access to the representation of one's own body-effectors on bodily self-awareness, in first-episode schizophrenia (FES) patients and healthy controls (HCs). We contrasted their performance in an implicit self-recognition task (visual matching) and in an explicit self/other discrimination task. Both tasks employed participant's own and others' body-effectors. Concerning the implicit task, HCs were more accurate with their own than with others' body-effectors, whereas patients did not show such self-advantage. Regarding the explicit task, both groups did not exhibit a self-advantage, and patients showed a higher percentage of self-misattribution errors. Neither self/other nor implicit/explicit effects were found in both groups when processing inanimate-objects. We propose that FES patients suffer of a disturbed implicit sense of bodily self.     

Finger counting habit and spatial–numerical association in children and adults

Sensory-motor experiences are known to build up concrete and abstract concepts during the lifespan. The present study aimed to test how finger counting habits (right-hand vs. left-hand starters) could influence the spatial–numerical representation in number-to-position (explicit) and digit-string bisection (implicit) tasks. The subjects were Italian primary school children (N = 184, from the first to the fifth year) and adults (N = 42). No general preference for right- or left-starting in the finger counting was found. In the explicit task, right- or left-starting did not affect performance. In the implicit task, the right-hand starters shifted from the left to the right space when bisecting small and large numbers respectively, while the left-hand starters shifted from the right to the left space with higher leftward bias for large numbers. The finger configuration in Italian children and adults influences the spatial–numerical representation, but only when implicit number processing is required by the task.     

Intrahemispheric visual-motor information processing and cerebral functional lateralization.

A series of stimuli, words and faces, were presented tachistoscopically to 24 dextrals and 12 sinistrals. The stimuli were presented to one eye at a time and the subjects were instructed to respond to specific words or stimuli with a specific hand. The results indicate that (1) cerebral functional asymmetry is related to handedness; in the dextrals, the left hemisphere is more specialized in verbal recognition, while in the sinistrals, the right hemisphere is more specialized in recognizing non-verbal material. (2) An ipsilateral hand-and-eye combination is a valid method of measuring intrahemispheric information processing, provided that the tachistoscopically presented visual stimuli are capable of inciting specialized hemispheric function. The dominant relationship among the crossed and non-crossed visual pathways is discussed.     

Aging affects word-stem completion and recognition but not category generation

In this study, we investigated the effect of aging on two implicit memory tasks, word-stem completion and category generation, and on explicit recognition. We compared the performance of young and older adults on these implicit memory tasks with those of explicit recognition. We expected better performance of young than older adults in the explicit memory task and similar priming in both implicit memory tasks. The results showed that young adults performed better than older adults in the recognition task. Moreover, both age groups showed priming in the implicit memory tasks, although priming was greater in young adults compared to older adults in the word-stem completion memory task, whereas both age groups showed similar levels of priming in the category generation task. The present results showed dissociations as a function of age not only between the explicit and the implicit tasks but also between the implicit tasks.     

Implicit and explicit learning: individual differences and IQ

We explored the degree to which individual differences in performance were observed in a group of subjects who worked with two different tasks: one implicit and one explicit. The implicit task was a standard artificial grammar-learning task; the explicit was a series-completion problem-solving task. Substantial individual differences were found between subjects on the explicit task; relatively small individual differences were found on the implicit task. Moreover, performance on the explicit task correlated strongly with intelligence quotient, but performance on the implicit task did not. Data from previous experiments were also found to be in agreement with these results. The findings are presented in the context of a general theory of implicit learning proposed recently by Reber (1989a, in press) that derives from considerations of the evolution of cognitive processes. This evolutionary model argues that unconscious, implicit induction systems are evolutionarily older and antedate conscious, explicit learning processes, and that this antiquity carries with it particular patterns of function that differentiate implicit processes from explicit processes.     

Autoscopic phenomena and one's own body representation in dreams

Autoscopic phenomena (AP) are complex experiences that include the visual illusory reduplication of one’s own body. From a phenomenological point of view, we can distinguish three conditions: autoscopic hallucinations, heautoscopy, and out-of-body experiences. The dysfunctional pattern involves multisensory disintegration of personal and extrapersonal space perception. The etiology, generally either neurological or psychiatric, is different. Also, the hallucination of Self and own body image is present during dreams and differs according to sleep stage. Specifically, the representation of the Self in REM dreams is frequently similar to the perception of Self in wakefulness, whereas in NREM dreams, a greater polymorphism of Self and own body representation is observed. The parallels between autoscopic phenomena in pathological cases and the Self-hallucination in dreams will be discussed to further the understanding of the particular states of self awareness, especially the complex integration of different memory sources in Self and body representation.     

Implicit and explicit memory for visual patterns

The article reports an investigation of implicit and explicit memory for novel, visual patterns. Implicit memory was assessed by a speeded perception task, and explicit memory by a four-alternative, forced-choice recognition task. Tests were given either immediately after testing or 7 days later. The results suggest that a single exposure of a novel, nonverbal stimulus is sufficient to establish a representation in memory that is capable of supporting long-lived perceptual priming. In contrast, recognition memory showed significant loss over the same delay. Performance measures in the two tasks showed stochastic independence on the first trial after a single exposure to each pattern. Finally, a specific occurrence of a previously studied item could be retrieved from explicit memory but did not affect the accuracy of perception in the implicit memory test. The results extend the domain of experimental dissociations between explicit and implicit memory to include novel, nonverbal stimuli.     

A performance measure of the degree of hand preference

The present paper describes a performance method for determining hand preference. The task requires participants to reach into different regions of hemispace to perform various actions (point, pick up, toss, sweep, and position) with a dowel located at each position. In accordance with the participants' hand preference as measured by the Waterloo Handedness Questionnaire, the preferred hand was used more frequently on the various performance tasks. The distribution of hand use in working space indicates that preferred hand use was almost exclusive for actions carried out in ipsilateral hemispace, while it is used only moderately for actions in contralateral hemispace, revealing that this hand is used throughout a wider range of extrapersonal space than the nonpreferred hand. These trends were observed across all of the performance tasks, suggesting that task complexity did not affect the frequency of preferred hand use either overall or, more specifically, in right hemispace, as was predicted. This finding is inconsistent with empirical work on questionnaires indicating that verbal reports of preferred hand use increase for more complex tasks (e.g., Steenhuis & Bryden, 1988). As well, performance on the preferential reaching task correlated significantly with hand preference as measured on the Waterloo Handedness Questionnaire (Bryden, 1977), unlike the other performance measure examined, indicating that the preferential reaching task is sensitive to differences in the degree of hand preference.     

The effects of skill demands and object position on the distribution of preferred hand reaches

Performance-based measures of hand preference have been developed as an objective method of examining handedness. Previous research using this method showed that both skill demands and the position of the object in working space affect preferential hand reaching. Specifically, preferred hand reaches predominated in left hemispace, in spite of the biomechanical inefficiency involved in reaching across the body midline. This was mediated by the skill demands, with a higher frequency of preferred hand reaches for tasks requiring more skill. To further examine this issue, we increased the task skill demands. Twenty-two right-handed adults reached for five tools located in an array of five positions in front of them. Participants were required to pick up the tool, pick up and demonstrate how to use it, or pick up and actually use the tool on the materials provided. The results showed that the frequency of right hand reaches was greatest for the tool use condition. This effect was mediated by the position of the object in hemispace, with more right hand reaches occurring for the Use task in left hemispace than the other tasks, in support of our previous work.     

Relationships between implicit and explicit uncertainty monitoring and mindreading: Evidence from autism spectrum disorder

We examined performance on implicit (non-verbal) and explicit (verbal) uncertainty-monitoring tasks among neurotypical participants and participants with autism, while also testing mindreading abilities in both groups. We found that: (i) performance of autistic participants was unimpaired on the implicit uncertainty-monitoring task, while being significantly impaired on the explicit task; (ii) performance on the explicit task was correlated with performance on mindreading tasks in both groups, whereas performance on the implicit uncertainty-monitoring task was not; and (iii) performance on implicit and explicit uncertainty-monitoring tasks was not correlated. The results support the view that (a) explicit uncertainty-monitoring draws on the same cognitive faculty as mindreading whereas (b) implicit uncertainty-monitoring only test first-order decision making. These findings support the theory that metacognition and mindreading are underpinned by the same meta-representational faculty/resources, and that the implicit uncertainty-monitoring tasks that are frequently used with non-human animals fail to demonstrate the presence of metacognitive abilities.     

Performance in haptic geometrical matching tasks depends on movement and position of the arms

Previous research on the properties of haptic space has shown systematic deviations from Euclidean parallelity in haptic parallelity tasks. The mainstream explanation for these deviations is that, in order to perform the task, participants generate a spatial representation with a frame of reference that integrates egocentric and allocentric components. Several studies have shown that the amount and type of deviations are affected by the configurations with regard to the arms and the rods to be matched. The present study reports 4 experiments that further address the effects of task configurations and body movements. Experiments 1 and 2 replicate and extend previous results concerning haptic matching task and acoustic pointing tasks. The third experiment includes acoustic cues aligned differentially to the reference and test bars. The fourth experiment concerns a geometrical matching task performed in the rear peripersonal space. Results show that haptic deviations from the Euclidean space are modulated by the available cues and by the body configurations. This indicates the need for further analysis on the role of body, arm and shoulder positions, and movement effects in haptic space perception.     

Auditory space perception in left- and right-handers

Several studies have shown that handedness has an impact on visual spatial abilities. Here we investigated the effect of laterality on auditory space perception. Participants (33 right-handers, 20 left-handers) completed two tasks of sound localization. In a dark, anechoic, and sound-proof room, sound stimuli (broadband noise) were presented via 21 loudspeakers mounted horizontally (from 80° on the left to 80° on the right). Participants had to localize the target either by using a swivel hand-pointer or by head-pointing. Individual lateral preferences of eye, ear, hand, and foot were obtained using a questionnaire. With both pointing methods, participants showed a bias in sound localization that was to the side contralateral to the preferred hand, an effect that was unrelated to their overall precision. This partially parallels findings in the visual modality as left-handers typically have a more rightward bias in visual line bisection compared with right-handers. Despite the differences in neural processing of auditory and visual spatial information these findings show similar effects of lateral preference on auditory and visual spatial perception. This suggests that supramodal neural processes are involved in the mechanisms generating laterality in space perception.     

Thinking high but feeling low: An exploratory cluster analysis investigating how implicit and explicit spider fear co-vary

Research has demonstrated large differences in the degree to which direct and indirect measures predict each other and variables including behavioural approach and attentional bias. We investigated whether individual differences in the co-variance of “implicit” and “explicit” spider fear exist, and whether this covariation exerts an effect on spider fear-related outcomes. One hundred and thirty-two undergraduate students completed direct and indirect measures of spider fear/avoidance, self-report questionnaires of psychopathology, an attentional bias task, and a proxy Behavioural Approach Task. TwoStep cluster analysis using implicit and explicit spider fear as criterion variables resulted in three clusters: (1) low explicit/low implicit; (2) average explicit/high implicit; and (3) high explicit/low implicit. Clusters with higher explicit fear demonstrated greater disgust propensity and sensitivity and less willingness to approach a spider. No differences between clusters emerged on anticipatory approach anxiety or attentional bias. We discuss results in terms of dual-systems and cognitive–behavioural models of fear.     

Hand dominance influences the processing of observed bodies

In motor tasks, subgroups of lefthanders have been shown to differ in the distribution of attention about their own bodies. The present experiment examined whether similar attentional biases also apply when processing observed bodies. Sixteen right handers (RHs), 22 consistent left handers (CLHs) and 11 relatively ambidextrous inconsistent left handers (ILHs) performed an own body transformation task in which they were instructed to make speeded left–right judgements about a schematic human figure. Attentional biases associated with handedness were found to extend to observed bodies: CLHs’ judgements were faster to the figure’s left side, while ILHs, like RHs, showed facilitated performance to the figure’s right side. These results demonstrate a novel embodiment effect whereby the processing of a static schematic human figure is modulated by an individual’s personal motor capabilities. This finding suggests that motor simulation may contribute to whole body perception in the absence of actual or implied actions.     

Exaggerated leftward bias in the mental number line of patients with schizophrenia

Several visuo-motor tasks can be used to demonstrate biases towards left hemispace in schizophrenic patients, suggesting a minor right hemineglect. Recent studies in neglect patients used a new number bisection task to highlight a lateralized defect in their visuo-spatial representation of numbers. To test a possible lateralized representational deficit in schizophrenia, we used the number bisection task in 11 schizophrenic patients compared to 11 healthy controls. Participants were required to orally indicate the central number of an interval orally presented. Whereas healthy subjects showed no significant bias, schizophrenic patients presented a significant leftward bias. Therefore, these results suggest an impairment in higher order representations of the number space in patients with schizophrenia, an impairment that is qualitatively similar to the deficit described in neglect patients.     

Aversive racism and medical interactions with Black patients: A field study

Medical interactions between Black patients and nonBlack physicians are usually less positive and productive than same-race interactions. We investigated the role that physician explicit and implicit biases play in shaping physician and patient reactions in racially discordant medical interactions. We hypothesized that whereas physicians’ explicit bias would predict their own reactions, physicians’ implicit bias, in combination with physician explicit (self-reported) bias, would predict patients’ reactions. Specifically, we predicted that patients would react most negatively when their physician fit the profile of an aversive racist (i.e., low explicit-high implicit bias). The hypothesis about the effects of explicit bias on physicians’ reactions was partially supported. The aversive racism hypothesis received support. Black patients had less positive reactions to medical interactions with physicians relatively low in explicit but relatively high in implicit bias than to interactions with physicians who were either: (a) low in both explicit and implicit bias, or (b) high in both explicit and implicit bias.     

Effect of environmental support on implicit and explicit memory in younger and older adults.

The study addressed 2 major issues: whether there are age differences on an implicit word-stem-completion task and whether age differences on both implicit and explicit memory would decrease with increased environmental support. A total of 287 Ss were presented with words in an incidental learning task with structural or semantic processing. Following 2 filler tasks, Ss received an implicit or an explicit word-stem-completion task. The number of letters in the stem varied from 2 to 4. Results yielded an Age x Memory Task dissociation such that there were large age differences on the explicit task and no age difference on the implicit task, regardless of whether Ss aware of the memory test were included or excluded. There was no evidence that environmental support improved older adults' performance more than that of younger adults on either memory task.     

Look,no hands: A perceptual task shows that number magnitude induces shifts of attention

The mental representation of numbers along a line oriented left to right affects spatial cognition, facilitating responses in the ipsilateral hemispace (the spatial-numerical association of response codes [SNARC] effect). We investigated whether the number/space association is the result of an attentional shift or response selection. Previous research has often introduced covert left/right response cues by presenting targets to the left or the right. The present study avoided left/right cues by requiring forced choice upper/lower luminance discriminations to two mirror-reversed luminance gradients (the grayscale task). The grayscale stimuli were overlaid with strings of (1) low numbers, (2) high numbers, and (3) nonnumerical characters. In Experiment 1, 20 dextrals judged the number’s magnitude and then indicated whether the upper/lower grayscale was darker. Results showed leftward and rightward attentional biases for low and high numbers, respectively. Demands to process numbers along a left/right line were made less explicit in Experiment 2 (N=8 dextrals), using (1) a parity judgment and (2) arbitrary linguistic labels for top/bottom. Once again, a spatial congruency effect was observed. Because the response (up/down) was orthogonal to the dimension of interest (left/right), the effect of number cannot be attributed to late-stage response congruencies. This study required unspeeded responses to stimuli presented in free vision, whereas other experiments have used speeded responses. Understanding the time course of number-space effects may, therefore, be important to the debate associated with response selection.