Dichaptic-visual form matching in adults

Although previous visuo-dichaptic matching studies report hemispheric asymmetries in spatial-form perception, more recent studies have failed to support these findings. Three cross-modal matching experiments examined hemispheric asymmetries in adult spatial-form matching. In the first experiment, subjects simultaneously felt two eight-point or 12-point tactile shapes patterned after Vanderplas and Garvin (1959) for four seconds and were then required to identify both shapes from a visual response array. Results showed subjects were significantly better identifying eight point shapes. A marginally significant feeling hand by pointing hand interaction indicated that recognition accuracy was higher when shape ipsilateral to the pointing hand was identified. In the second experiment, only one of the two tactile shapes had to be identified from the visual array. Results showed a significant interaction between complexity and feeling hand, where the left and right feeling hands were respectively better at identifying 12-point and eight-point shapes. The third experiment was an attempt to more directly examine the Witelson (1976) experiment using her spatial-form stimuli. Results showed no significant laterality nor stimulus-response compatibility effects. These findings are discussed in terms of cerebral asymmetry and stimulus-response compatibility models.     

Touching base: The effect of participant and stimulus modulation factors on a haptic line bisection task

Acquiring information about our environment through touch is vital in everyday life. Yet very little literature exists about factors that may influence haptic or tactile processing. Recent neuroimaging studies have reported haptic laterality effects that parallel those reported in the visual literature. With the use of a haptic variant of the classical line bisection task, the present study aimed to determine the presence of laterality effects on a behavioural level. Specifically, three handedness groups including strong dextrals, strong sinistrals, and-the to-date largely neglected group of-mixed-handers were examined in their ability to accurately bisect stimuli constructed from corrugated board strips of various lengths. Stimulus factors known to play a role in visuospatial perception including stimulus location, the hand used for bisection, and direction of exploration were systematically varied through pseudo-randomisation. Similar to the visual domain, stimulus location and length as well as participants' handedness and the hand used for bisection exerted a significant influence on participants' estimate of the centre of haptically explored stimuli. However, these effects differed qualitatively from those described for the visual domain, and the factor direction of exploration did not exert any significant effect. This indicates that laterality effects reported on a neural level are sufficiently pronounced to result in measurable behavioural effects. The results, first, add to laterality effects reported for the visual and auditory domain, second, are in line with supramodal spatial processing and third, provide additional evidence to a conceptualisation of pseudoneglect and neglect as signs of hemispheric attentional asymmetries.     

Haptic orientation perception: sex differences and lateralization of functions

The present study examined sex differences in haptic orientation representation using three tasks: a bimanual parallel-setting task comprising haptic orientation perception and motor matching action, and two unimanual tasks focusing on the perception and action elements separately. A verbal judgment task focused on haptic orientation perception: participants were to assign a number of minutes to a felt orientation. An orientation production task required the rotation of a bar to match a verbally presented number of minutes. Although both male and female performance was systematically biased we found that males are more accurate in parallel-setting and verbal judgment of orientation, suggesting differences in haptic orientation perception, in particular. Increasing allocentric reference frame involvement by delaying the action in the parallel-setting task did not affect the sex difference found. In addition to a male advantage over tasks, performance on both unimanual tasks suggests sex differences in lateralization of haptic orientation processing; a dependence on hand orientation was found only for right hand performance in males.     

Touching base: The effect of participant and stimulus modulation factors on a haptic line bisection task

Acquiring information about our environment through touch is vital in everyday life. Yet very little literature exists about factors that may influence haptic or tactile processing. Recent neuroimaging studies have reported haptic laterality effects that parallel those reported in the visual literature. With the use of a haptic variant of the classical line bisection task, the present study aimed to determine the presence of laterality effects on a behavioural level. Specifically, three handedness groups including strong dextrals, strong sinistrals, and—the to-date largely neglected group of—mixed-handers were examined in their ability to accurately bisect stimuli constructed from corrugated board strips of various lengths. Stimulus factors known to play a role in visuospatial perception including stimulus location, the hand used for bisection, and direction of exploration were systematically varied through pseudo-randomisation. Similar to the visual domain, stimulus location and length as well as participants' handedness and the hand used for bisection exerted a significant influence on participants' estimate of the centre of haptically explored stimuli. However, these effects differed qualitatively from those described for the visual domain, and the factor direction of exploration did not exert any significant effect. This indicates that laterality effects reported on a neural level are sufficiently pronounced to result in measurable behavioural effects. The results, first, add to laterality effects reported for the visual and auditory domain, second, are in line with supramodal spatial processing and third, provide additional evidence to a conceptualisation of pseudoneglect and neglect as signs of hemispheric attentional asymmetries.     

What do lateralized displays tell us about visual word perception? A cautionary indication from the word-letter effect

A common assumption underlying laterality research is that visual field asymmetries in lateralized word perception indicate the hemispheric specialisation of processes generally available for the perception of words, including words viewed in a more typical setting (i.e. in the central visual field). We tested the validity of this assumption using a phenomenon (the word-letter effect) frequently reported for displays viewed in the central visual field, where letters in words are perceived more accurately than the same letters in isolation. Words and isolated letters were presented in the left visual field (LVF), right visual field (RVF) and central visual field (CVF), the Reicher-Wheeler task was used to suppress influences of guesswork, and an eye-tracker ensured central fixation. In line with previous findings, lateralized displays revealed a RVF-LVF advantage for words (but not isolated letters) and CVF displays revealed an advantage for words over isolated letters (the word-letter effect). However, RVF and LVF displays both produced an advantage for isolated letters over words (a letter-word effect), indicating that processing subserving the advantage for words when participants viewed stimuli in the central visual field was unavailable for lateralized displays. Implications of these findings for studies of lateralized word perception are discussed.     

Effects of blurring and stimulus size on the lateralized processing of nonverbal stimuli

Right-handed subjects indicated whether two novel, nonlinguistic stimuli were physically identical or not. In Experiment 1 blurring these stimuli impaired performance when stimuli were projected to the right visual field but not when stimuli were projected to the left visual field. This lateralized effect of blurring is similar to earlier findings in letter-matching experiments and indicates that such effects do not depend on hemispheric differences in verbal mediation. Experiment 2 examined the lateralized effects of stimulus size using the same task as Experiment 1. The pattern of results from this experiment suggests that both visual spatial frequency and stimulus perceptibility contribute to interactions of stimulus clarity and visual field and that neither factor by itself may be the sole determinant of the lateralized effects of input variables.     

Manual laterality in haptic and visual reaching tasks by tufted capuchin monkeys (Cebus apella). An association between hand preference and hand accuracy for food discrimination

Manual laterality was examined in 26 tufted capuchins (Cebus apella) in three tasks differing in their sensorimotor demands and the availability of visual cues. The Haptic discrimination task required the monkeys to discriminate haptically between two pumpkin seeds and two tinfoil items stuck into a tray inside an opaque box. The other two tasks required the monkeys to reach for two pumpkin seeds stuck into the tray within a transparent box with vision (Visually guided reaching task) or without vision (Visual-Tactual reaching task) during reaching. A significant group-level left hand bias was found for food retrieval in both the Haptic discrimination and Visual-Tactual tasks, and a significant group-level right hand bias in the Visually guided reaching task. The strength of hand preferences did not differ among the tasks. It was found that the accuracy of food recognition in the Haptic discrimination task was greater for the left than the right hand. The results suggest that the differences in the manipulo-spatial requirements of the tasks and in the availability of visual cues can variously affect manual laterality in capuchins. The left-hand preferences for the Haptic discrimination and Visual-Tactual tasks as well as the left-hand advantage for food discrimination may reflect a greater involvement of the right hemisphere in processing haptic information.     

Motor and visual imagery as two complementary but neurally dissociable mental processes.

Recent studies indicate that covert mental activities, such as simulating a motor action and imagining the shape of an object, involve shared neural representations with actual motor performance and with visual perception, respectively. Here we investigate the performance, by normal individual and subjects with a selective impairment in either motor or visual imagery, of an imagery task involving a mental rotation. The task involved imagining a hand in a particular orientation in space and making a subsequent laterality judgement. A simple change in the phrasing of the imagery instructions (first-person or third-person imagery) and in actual hand posture (holding the hands on the lap or in the back) had a strong impact on response time (RT) in normal subjects, and on response accuracy in brain-damaged subjects. The pattern of results indicates that the activation of covert motor and visual processes during mental imagery depends on both top-down and bottom-up factors, and highlights the distinct but complementary contribution of covert motor and visual processes during mental rotation.     

Division of labor between hand and eye when perceiving shape

Earlier research has shown that young children rely almost exclusively on visual inspection of shape in a situation where both haptic and visual perception may be combined. The present investigation sought to determine whether adults would perform similarly, or whether, with development, information acquisition strategies change such that both haptic and visual sources would be combined. Results clearly showed that adults did combine haptic and visual pickup where matching was with haptic comparison shapes. But, where matching was with visual comparisons, information pickup was confined to visual inspection.     

Differences in visual attention and task interference between males and females reflect differences in brain laterality

Two cognitive tasks (a letter memory task and a spatial memory task) designed to selectively activate the left or right hemisphere were combined with attentional probe tasks to measure how hemispheric activation affects attention to left and right hemifields. The probe task in Experiment 1 required the identification of digits in the left and right hemifield. During the letter task, male subjects identified more probes from the left hemifield than from the right. Their accuracy varied little across the two hemifields during the dots task.Experiment 2 tested whether this pattern is due to either spatial attention or interference in character processing. Instead of identifying digits, the probe task required subjects to respond to a black square that appeared in the periphery of the screen. For male subjects, the pattern was opposite of that from Experiment 1. During the letter task they responded faster to the probe in the right hemifield than in the left. Their response times were equivalent across the two hemifields during the dots task.These results indicate two separate effects of laterality in male subjects. The activation of one hemisphere produced more attention to the contralateral hemifield in Experiment 2, and the letter memory task interfered with the processing of other characters in the right visual field more than those in the left visual field in Experiment 1. Neither of these effects appeared in female subjects, corroborating earlier claims that female brains are less lateralized than male brains.     

Manual laterality in haptic and visual reaching tasks by tufted capuchin monkeys (Cebus apella). An association between hand preference and hand accuracy for food discrimination

Manual laterality was examined in 26 tufted capuchins (Cebus apella) in three tasks differing in their sensorimotor demands and the availability of visual cues. The Haptic discrimination task required the monkeys to discriminate haptically between two pumpkin seeds and two tinfoil items stuck into a tray inside an opaque box. The other two tasks required the monkeys to reach for two pumpkin seeds stuck into the tray within a transparent box with vision (Visually guided reaching task) or without vision (Visual-Tactual reaching task) during reaching. A significant group-level left hand bias was found for food retrieval in both the Haptic discrimination and Visual-Tactual tasks, and a significant group-level right hand bias in the Visually guided reaching task. The strength of hand preferences did not differ among the tasks. It was found that the accuracy of food recognition in the Haptic discrimination task was greater for the left than the right hand. The results suggest that the differences in the manipulo-spatial requirements of the tasks and in the availability of visual cues can variously affect manual laterality in capuchins. The left-hand preferences for the Haptic discrimination and Visual-Tactual tasks as well as the left-hand advantage for food discrimination may reflect a greater involvement of the right hemisphere in processing haptic information.     

The effect of response mode on lateralized lexical decision performance

We examined the effect of manipulations of response programming, i.e. post-lexical decision making requirements, on lateralized lexical decision. Although response hand manipulations tend to elicit weaker laterality effects than those involving visual field of presentation, the implementation of different lateralized response strategies remains relatively unexplored. Four different response conditions were compared in a between-subjects design: (1) unimanual, (2) bimanual, (3) congruent visual field/response hand, and (4) confounded response hand/target lexicality response. It was observed that hemispheric specialization and interaction effects during the lexical decision task remained unchanged despite the very different response requirements. However, a priori examination of each condition revealed that some manipulations yielded a reduced power to detect laterality effects. The consistent observation of left hemisphere specialization, and both left and right hemisphere lexicality priming effects (interhemispheric transfer), indicate that these effects are relatively robust and unaffected by late occurring processes in the lexical decision task. It appears that the lateralized response mode neither determines nor reflects the laterality of decision processes. In contrast, the target visual half-field is critical for determining the deciding hemisphere and is a sensitive index of hemispheric specialization, as well as of directional interhemispheric transfer.     

The function of inferoparietal cortex during cross-modal matching in the monkey: Analysis of event-related potentials

Transcortical evoked potentials (EP's) were collected while monkeys performed a haptic to visual matching task. EP's were sorted into “sample” groups, according to the haptic stimuli, “match” groups, according to the choice of a visual alternative, and “spatial” groups, depending upon the panel (right or left) pressed during the matching response. Electrodes in inferoparietal cortex yielded event-related activity due to the matching and spatial aspects of responding, but not to haptic sampling. A postcentral electrode yielded event-related differences due to haptic sampling and spatial response, and a smaller difference related to visual matching. Implications for the neural mediation of cross-modal operations are discussed.     

Neural specialization for letter recognition

Functional magnetic resonance imaging (fMRI) was used to estimate neural activity while subjects viewed strings of consonants, digits, and shapes. An area on or near the left fusiform gyrus was found that responded significantly more to letters than digits. Similar results were obtained when consonants were used whose visual features were matched with the digits and when an active matching task was used, suggesting that the results cannot be easily attributed to artifacts of the stimuli or task. These results demonstrate that neural specialization in the human brain can extend to a category of stimuli that is culturally defined and that is acquired many years postnatally.     

Depression, pain, and hemispheric activation

The present study attempts to delineate the role of hemispheric activation in depression and pain. It was hypothesized that the right hemisphere is specialized to become activated by and to process negative affective stimuli, and that this specialization may play a role in the co-occurrence of depression and pain. The relationship between depression, experimental pain, and cerebral laterality was investigated in 16 depressed and 16 nondepressed, right-handed, female students. Cerebral laterality was measured via tasks assessing visual and auditory biases, and pain was assessed via a cold pressor task. The proposition that the right hemisphere mediates the co-occurrence of pain and depression was not supported, but specific findings did suggest that the right hemisphere may play a unique role in pain perception. Data from the visual task indicated that prior exposure to pain results in increased right hemisphere activation as indicated by a left visual field bias. Pain perception was a complex function of mood, preceding tasks, and the hand tested, and it was suggested that exposure to a typical right-hemisphere task increased the left side lateralization of pain in nondepressed subjects. Implications of these findings are discussed for coexisting problems of pain and depression and for the lateralization of pain in disorders judged to involve a significant psychogenic component.     

Association between auditory and visual symptoms of unilateral spatial neglect

Unilateral spatial neglect due to right brain damage (RBD) can occur in several different sensory modalities in the same patient. Previous studies of the association between auditory and visual neglect have yielded conflicting outcomes. Most such studies have compared performance on relatively simple clinical measures of visual neglect, such as target cancellation, with that on more sophisticated measures of auditory perception. This is problematic because such tasks are typically not matched for the cognitive processes they exercise. We overcame this limitation by using equivalent visual and auditory versions of extinction and temporal-order judgment (TOJ) tasks. RBD patients demonstrated lateralized deficits on both visual and auditory tasks when compared with same-aged, healthy controls. Critically, a significant association between the severity of visual and auditory deficits was apparent on the TOJ task but not the extinction task, suggesting that even when task demands are matched across modalities, dissociations between visual and auditory neglect can be apparent. Across the auditory tasks, patients showed more pronounced deficits for verbal stimuli than for non-verbal stimuli. These findings have implications for recent models proposed to explain the role of spatial attention in multimodal perception.     

The traffic light paradigm: a reaction time task to study laterally directed arm movements

Patients with unilateral brain damage may show slowed or hypometric arm movements toward the contralesional space, as compared to movements directed towards the side of the brain lesion. The present article describes a reaction time paradigm devised to study accuracy and latency of directional arm movements in normal human subjects and brain-damaged patients. Experimental paradigms hitherto used to explore directional motor disorders often do not reliably disentangle between perceptual and motor factors, because they employ lateralized perceptual stimuli. The traffic light paradigm, instead, consists of visual stimuli presented on the vertical midline (like a traffic light) and hand responses to be produced in either hemispace. Thus, participants have to produce lateralized arm responses to central visual stimuli. Performance on this 'motor' paradigm can be contrasted with performance on a 'perceptual' reaction time task, consisting of similar, but lateralized visual stimuli and central motor responses. Results obtained with these paradigms on normal participants and brain-damaged patients are presented and discussed. These results give empirical support to the claim that the traffic light paradigm is suitable to study directional motor disorders in relative isolation from perceptual biases.     

Lateralized interference in finger tapping: Assessment of block design activities

Dual task procedures were used to evaluate lateralized processing of block design solutions. Right-handed college students tapped a micro-key alone vs tapped while solving block design problems. Lateralized interference, implicating right-hemisphere processing, was observed when subjects manually completed block designs with their non-tapping hand. When manual block manipulation was not required and subjects solved designs mentally, a different laterality pattern suggesting left-hand facilitation in conjunction with right-hand interference in tapping performance was observed. Only the facilitation effect, however, was reliably different from zero.     

Dual functional hemispheric asymmetry in visual perception: Effects of ocular dominance and postexposural processes

The authors investigated laterality differences in visual perception by assessing the effects of the directional post-exposure scanning movements associated with reading habits, the visual half-field (VHF) in which stimuli were presented, and eye dominance on an immediate recall task. Forty Chinese bilingual subjects (20 right-eye dominant and 20 left-eye dominant) were tested for their recall of forms, Chinese words and English words. The stimuli were projected tachistoscopically in the left and/or right VHFs under conditions of simulataneous and successive presentation. The results demonstrated a right field superiority for verbal stimuli under both conditions and a left field superiority for nonverbal stimuli when presented successively. Right-eyed subjects were better in processing verbal materials and left-eyed subjects were better in the perception and recall of nonverbal materials. The study supported the validity of the psychophysiological model of asymmetrical cerebral functioning and demonstrated the importance of reading habits and eye dominance. The findings were interpreted as preliminary support for Piaget's postulated relationship between perceptual and organic development.     

Exploring laterality and memory effects in the haptic discrimination of verbal and non-verbal shapes

The brain’s left hemisphere often displays advantages in processing verbal information, while the right hemisphere favours processing non-verbal information. In the haptic domain due to contra-lateral innervations, this functional lateralization is reflected in a hand advantage during certain functions. Findings regarding the hand-hemisphere advantage for haptic information remain contradictory, however. This study addressed these laterality effects and their interaction with memory retention times in the haptic modality. Participants performed haptic discrimination of letters, geometric shapes and nonsense shapes at memory retention times of 5, 15 and 30?s with the left and right hand separately, and we measured the discriminability index d′. The d′ values were significantly higher for letters and geometric shapes than for nonsense shapes. This might result from dual coding (naming?+?spatial) or/and from a low stimulus complexity. There was no stimulus-specific laterality effect. However, we found a time-dependent laterality effect, which revealed that the performance of the left hand-right hemisphere was sustained up to 15?s, while the performance of the right-hand-left hemisphere decreased progressively throughout all retention times. This suggests that haptic memory traces are more robust to decay when they are processed by the left hand-right hemisphere.