The effects of complexity on the perception of vibrotactile patterns presented to separate fingers.

Pairs of vibrotactile patterns were presented to subjects' left middle and index fingerpads (unilateral presentation) or left and right index fingerpads (bilateral presentation), using two Optacon arrays. A set of simple (one-line) patterns and a set of complex (two-line) patterns were constructed so that they were equally identifiable when presented individually. In Experiment 1, discrimination performance was lower for two-line patterns than it was for one-line patterns, and it was lower for unilateral presentation than it was for bilateral presentation. Communality, the number of lines that two patterns share in common, was a major factor in reducing discrimination performance for two-line patterns. Subjects' abilities to identify one member of the pair of patterns were measured in Experiment 2. There were no significant differences in performance between pattern sets or type of presentation when subjects attended to a single pattern. However, when subjects were required to attend to both patterns, identification performance was lower for two-line patterns than it was for one-line patterns, and it was lower for unilateral presentation than it was for bilateral presentation. The results suggest that there are limited attentional resources for processing vibrotactile patterns and that more resources are available bilaterally than are available unilaterally.     

The effects of complexity on the perception of vibrotactile patterns.

Vibrotactile patterns were presented to subjects' left index fingerpads using the array from the Optacon. A set of simple (one-line) patterns and a set of complex (two-line) patterns were constructed so that they were equally identifiable when presented individually. In Experiment 1, discrimination performance was lower for two-line patterns than for one-line patterns. Communality, the number of lines that two patterns share in common, appeared to be the major factor in reducing discrimination performance for two-line patterns. Experiment 2 measured the time required to identify individual patterns. There was no significant difference in identification times for one- and two-line patterns, suggesting that features within a pattern were processed simultaneously. In the presence of a temporal masking stimulus (Experiment 3), two-line patterns were more difficult to identify than one-line patterns, but reaction times were similar for the two sets of patterns. The results suggest that varying complexity affects perception of patterns at later stages of processing.     

The effects of complexity on the perception of vibrotactile patterns

Vibrotactile patterns were presented to subjects’ left index fmgerpads using the array from the Optacon. A set of simple (one-line) patterns and a set of complex (two-line) patterns were constructed so that they were equally identifiable when presented individually. In Experiment 1, discrimination performance was lower for two-line patterns than for one-line patterns. Communality, the number of lines that two patterns share in common, appeared to be the major factor in reducing discrimination performance for two-line patterns. Experiment 2 measured the time required to identify individual patterns. There was no significant difference in identification times for one- and two-line patterns, suggesting that features within a pattern were processed simultaneously. In the presence of a temporal masking stimulus (Experiment 3), two-line patterns were more difficult to identify than one-line patterns, but reaction times were similar for the two sets of patterns. The results suggest that varying complexity affects perception of patterns at later stages of processing.     

The effect of location on the discrimination of spatial vibrotactile patterns

The present study examined whether the locations of patterns on the skin affected the ability to process information about their shapes. In Experiment 1, pairs of spatial vibrotactile patterns, using the array from the Optacon, were presented sequentially to subjects’ left index fingerpads. The location of each pattern in a pair was varied randomly among four locations on the skin. The subjects responded “same” or “different” on the basis of the shapes of patterns, regardless of their locations. Discrimination accuracy was highest and response time fastest when patterns occupied identical locations (ILs), and performance suffered with increasing distance between patterns. In Experiment 2, pairs were presented to corresponding points or to noncorresponding points on separate fingerpads. When patterns occupied corresponding points on separate fingers, accuracy was lower than when patterns occupied ILs on a single finger, but higher than when patterns occupied noncorresponding points on separate fingers. The results suggested that discriminability declined partly because patterns did not occupy ILs, and partly because separate locations had different densities of innervation.     

Judgments of the duration of visually marked empty time intervals: Linking perceived duration and sensitivity

The capability of subjects to categorize (as short or long) visually marked empty time intervals was investigated in three experiments. Two visual signals, located 18° to the left (L) and to the right (R) of a fixation point in the visual field, established four marking conditions, two unilaterally presented (L-L and R-R) and two bilaterally presented (L-R and R-L). In Experiments 1 and 2, the results show that discrimination is better with unilateral sequences than with bilateral sequences and that the perceived duration is longer with an L-R than with an R-L sequence. In addition, Experiment 2 shows that, in comparison with a condition in which Markers 1 and 2 remain identical for a complete session, varying the markers from trial to trial does not decrease discrimination. Also, Experiment 2 shows that discrimination is better when both visual markers are presented at fovea than it is in the unilateral conditions. Experiment 3 shows that bilateral intervals are perceived as being longer and are better discriminated than are intervals marked by an intermodal sequence (auditory-visual or visual-auditory). The general discussion reports the implications of having different perceived duration and sensitivity levels, in various marker-type conditions, for an internal-clock hypothesis. Some implications of these results for a lateralized-timer hypothesis are also discussed.     

大脑两半球与整体和局部性质的选择性加工

研究大脑两半球在加工整体和局部性质中的优势以及两半球能否同时分别选择两个复合刺激的整体和局部性质。实验中把一个复合字母随机呈现在左视野或右视野,或者把两个复合字母同时分别呈现在左视野和右视野。实验一发现,在单侧呈现条件下,被试检测左右视野的整体或局部靶目标的反应时没有显著差别,但在双侧同时呈现条件下,检测右视野局部靶目标比检测左视野局部靶目标时的反应时短。实验二要求被试检测同时呈现在左右视野的整体或局部靶目标,发现当两个视野的靶目标处于同一水平时(整体或局部)反应时较短,两个视野的靶目标处于不同水平时(一侧处于整体水平而另一侧处于局部水平)反应时较长。这些结果提示,当两个复合刺激同时呈现在左右视野时,大脑左半球在选择性加工局部性质时具有优势;左右两半球更容易选择两个复合刺激同一个水平的性质,分别选择两个复合刺激不同水平的性质比较困难。     

Tactile pattern perception by two fingers: Temporal interference and response competition

The identification of a spatial pattern (target) presented to one fingerpad may be interfered with by the presentation of a second pattern (nontarget) to either the same fingerpad or a second fingerpad. A portion of the interference appears to be due to masking and a portion to response competition. In the present study, vibrotactile spatial patterns were designed to extend over two fingerpads. Target and nontarget patterns were presented to the same two fingerpads with a temporal separation between the two patterns. The function relating target identification to the temporal separation between the target and nontarget was very similar to the functions obtained with one-finger patterns in temporal masking studies. Subsequent measurements showed that a substantial portion of the interference resulted from response competition. Pattern categorization was better when patterns were presented to two fingers on opposite hands than to two fingers on the same hand; however, there was more interference for patterns presented bilaterally than for patterns presented ipsilaterally. The results supported the conclusion that similar processes are involved in the perception of sequences of spatial patterns whether the patterns are presented to one or to two fingers.     

Perceptual learning of spatiotemporal events: evidence from an unfamiliar modality

Perceptual learning was examined in two experiments in which subjects, originally unfamiliar with vibrotactile stimulation, were required to identify dynamic vibrotactile patterns with static visual patterns of the same two-dimensional shapes. In Experiment 1 we examined changes in performance with practice under a variety of vibrotactile spatial and temporal conditions. In Experiment 2 we investigated transfer of learning from one set of vibrotactile patterns to another different set. In neither experiment were subjects supplied with knowledge of results. Substantial perceptual learning (improvement in identification with practice) was observed in Experiment 1, although a minority of subjects did not exhibit improvement. Experiment 2 confirmed the general findings of Experiment 1 and also provided evidence of substantial positive transfer. In both experiments, multidimensional scaling of pattern confusion data revealed that practice (and improvement in identification) did not qualitatively change the relative confusability of patterns, suggesting that the (informative) structure of the patterns, irrespective of familiarity with a specific set of patterns, determined confusability. The findings are interpreted in terms of learning constructs offered by E. J. and J. J. Gibson. We conclude by considering the prospects that a connectionist mechanism can account for the observed perceptual learning.     

Vibrotactile pattern isolation/integration

Temporal integration has been cited as a major factor in temporal masking. Two experiments were designed to examine the conditions under which temporal integration may aid or hinder the perception of vibrotactile spatial patterns. In Experiment 1, the subject’s task was to discriminate between pairs of patterns. Each pattern was composed of two temporally separated pattern elements. When the task required the subjects to perceive the individual pattern elements, performance improved with temporal isolation—that is, performance improved as the temporal separation between the elements increased. In a second task, when the discrimination could be based on either the overall pattern shape or the pattern elements, temporal integration appeared to improve performance—that is, performance improved as the temporal separation decreased. In Experiment 2, an identification task was used. Several factors appeared to determine whether temporal integration aided or hindered pattern identification. When pattern elements similar to those in Experiment 1 were tested, performance improved with increasing temporal separation (isolation). A single function was fit to the discrimination (isolation) and identification (isolation) results. Whether temporal integration aids or hinders pattern perception appears to depend on pattern shape, the pattern elements, and the nature of the task.     

Temporal order and tactile patterns

Temporal order judgments (TOJs) were obtained for tactile stimuli presented to subjects' fingerpads. In one set of measurements, pairs of spatial patterns were presented successively to a single fingerpad (same-site condition), to two fingers on the same hand (ipsilateral condition), or to two fingers on opposite hands (bilateral condition). The subjects were instructed to report which one of the two patterns was presented first. TOJs were more accurate in the same-site condition than in either the ipsilateral or the bilateral conditions. In the ipsilateral and bilateral conditions, performance improved when judging which one of two locations received a stimulus first, although performance levels were still lower than in the same-site condition. Increasing the size of the pattern set from which the two patterns to be judged were drawn had only a slight effect on same-site performance and no effect on ipsilateral/bilateral performance; however, changing the nature of the patterns had a considerable effect on same-site performance and a smaller effect on ipsilateral/bilateral performance. Introducing an intensity imbalance between members of the pair of stimuli also had a large effect on same-site TOJs: a less intense stimulus tended to be judged as being presented first. In the bilateral condition, however, there was a small effect in the reverse direction: more intense stimuli tended to be judged as being presented first. The intensity imbalance had no effect in the ipsilateral condition. The results suggest that different mechanisms are responsible for TOJs for patterns presented to the same-site and to separate sites and, furthermore, that separate sites may constitute separate channels for spatial information.     

A comparison of discrimination and identification of vibrotactile patterns

Both discrimination and identification tasks have been used to assess subjects' abilities to perceive vibratory spatial patterns presented to the skin. The present study examined discrimination and identification performance under comparable conditions. In Experiment 1, subjects attempted to discriminate a pair of patterns on some blocks of trials and to identify both members of a pair on other blocks. For both tasks, the time between the members of the pair was varied. Discrimination performance could be predicted accurately from identification data. Analysis of performance on identification trials indicated that subjects used discriminability information to identify pairs. In Experiment 2, discrimination and identification were compared when the temporal separation between patterns was fixed and a masking stimulus followed each pattern after a variable delay. Results suggest that temporal masking, rather than the time available for processing pattern information, is the major limitation in both discrimination and identification of sequences of tactile patterns.     

Interhemispheric cooperation and non-cooperation during word recognition: evidence for callosal transfer dysfunction in dyslexic adults

Participants report briefly-presented words more accurately when two copies are presented, one in the left visual field (LVF) and another in the right visual field (RVF), than when only a single copy is presented. This effect is known as the 'redundant bilateral advantage' and has been interpreted as evidence for interhemispheric cooperation. We investigated the redundant bilateral advantage in dyslexic adults and matched controls as a means of assessing communication between the hemispheres in dyslexia. Consistent with previous research, normal adult readers in Experiment 1 showed significantly higher accuracy on a word report task when identical word stimuli were presented bilaterally, compared to unilateral RVF or LVF presentation. Dyslexics, however, did not show the bilateral advantage. In Experiment 2, words were presented above fixation, below fixation or in both positions. In this experiment both dyslexics and controls benefited from the redundant presentation. Experiment 3 combined whole words in one visual field with word fragments in the other visual field (the initial and final letters separated by spaces). Controls showed a bilateral advantage but dyslexics did not. In Experiments 1 and 3, the dyslexics showed significantly lower accuracy for LVF trials than controls, but the groups did not differ for RVF trials. The findings suggest that dyslexics have a problem of interhemispheric integration and not a general problem of processing two lexical inputs simultaneously.     

Visual sampling after lesions of the superior colliculus in rats

In two separate experiments, rats with bilateral lesions of the superior colliculus showed significantly poorer relearning of a horizontal/vertical stripe discrimination than control animals. In Experiment 1, all animals showed disruption of performance when a stimulus--response (S--R) separation was introduced by raising the stimuli above the site of responding. However, the colliculectomized rats were much more disturbed by the S--R separation than were animals in the control group. In Experiment 2, all animals showed lower performance levels when conflicting patterns were introduced into the upper portion of the stimulus doors, but this time the rats with collicular lesions were less disturbed than the control animals. It is suggested (a) that when the stimulus and response sites are discontiguous, animals must make an appropriate orienting response in order to effectively sample the visual stimuli and (b) that lesions of the superior colliculus alter performance by interfering with this orienting behavior. The impairment in relearning is tentatively attributed to the absence of preoperative overtraining on the discrimination task.     

Interactions between presentation modality and encoding task in frequency judgements

In two experiments, presentation modality of a list of items and encoding task were varied, and subjects judged the frequency with which certain words had been presented in the list. In Experiment 1, auditory presentation led to higher judgements of frequency than did visual presentation when subjects counted the consonants in the words but not when they rated imageability or when they kept a running count of the number of presentations of each word. In Experiment 2, encoding questions about the rhyme or spelling patterns of target words produced opposite effects for auditory and visual items. The results are interpreted as indicating that cross-modal translation during encoding produces a bias towards higher-frequency judgements and may also produce better frequency discrimination.     

Discriminating speech rhythms in audition,vision, and touch

We investigated the extent to which people can discriminate between languages on the basis of their characteristic temporal, rhythmic information, and the extent to which this ability generalizes across sensory modalities. We used rhythmical patterns derived from the alternation of vowels and consonants in English and Japanese, presented in audition, vision, both audition and vision at the same time, or touch. Experiment 1 confirmed that discrimination is possible on the basis of auditory rhythmic patterns, and extended it to the case of vision, using ‘aperture-close’ mouth movements of a schematic face. In Experiment 2, language discrimination was demonstrated using visual and auditory materials that did not resemble spoken articulation. In a combined analysis including data from Experiments 1 and 2, a beneficial effect was also found when the auditory rhythmic information was available to participants. Despite the fact that discrimination could be achieved using vision alone, auditory performance was nevertheless better. In a final experiment, we demonstrate that the rhythm of speech can also be discriminated successfully by means of vibrotactile patterns delivered to the fingertip. The results of the present study therefore demonstrate that discrimination between language's syllabic rhythmic patterns is possible on the basis of visual and tactile displays.     

Bilateral associations of low-level unilateral performance: an unremarked aspect of limb control

The experimenters examine upper limb movement discrimination performance in an arm-raising task for bilateral associations of low-level unilateral performance. On a cue from the experimenter, young adults (n = 23) with no history of shoulder injury raised either their left arm, right arm, or both together in a forward flexion movement until their hand or hands contacted an unseen, adjustable, overhead stop. The participant then judged which of the 5 possible stop positions, in the 12-20 degrees range forward of true vertical, the participant had contacted on the particular trial. Results showed that for the 16 participants whose best performance was in 1 of the unimanual conditions discrimination scores in the bilateral condition were equivalent to those of their worse-performing limb. For the 7 participants whose best discrimination performance was obtained on bimanual arm-raising, scores for the 2 unimanual conditions were equivalently low. Therefore, when a single limb that can perform well operates in conjunction with a limb performing at a lower level, the consequence is lowering the bimanual movement discrimination performance.     

Spatial constraints on visual-tactile cross-modal distractor congruency effects

Across three experiments, participants made speeded elevation discrimination responses to vibrotactile targets presented to the thumb (held in a lower position) or the index finger (upper position) of either hand, while simultaneously trying to ignore visual distractors presented independently from either the same or a different elevation. Performance on the vibrotactile elevation discrimination task was slower and less accurate when the visual distractor was incongruent with the elevation of the vibrotactile target (e.g., a lower light during the presentation of an upper vibrotactile target to the index finger) than when they were congruent, showing that people cannot completely ignore vision when selectively attending to vibrotactile information. We investigated the attentional, temporal, and spatial modulation of these cross-modal congruency effects by manipulating the direction of endogenous tactile spatial attention, the stimulus onset asynchrony between target and distractor, and the spatial separation between the vibrotactile target, any visual distractors, and the participant’s two hands within and across hemifields. Our results provide new insights into the spatiotemporal modulation of crossmodal congruency effects and highlight the utility of this paradigm for investigating the contributions of visual, tactile, and proprioceptive inputs to the multisensory representation of peripersonal space.     

Effects of type of cognitive demand on bilateral advantage in interhemispheric processing

The relationship between cognitive task demand and effect of bilateral advantage (BLA) was examined. In Experiment 1, the task demand based upon visual stimulus complexity was manipulated. One-digit and two-digit numbers were presented in the left, right or both visual fields tachistoscopically and subjects were requested to identify the numbers. The results showed no BLA, although a right visual field advantage was demonstrated. In Experiment 2, cognitive demand in terms of memory was manipulated. Subjects were asked to recall one-digit numbers that were presented successively once, three and five times in the left, right or the both visual fields. The results did not show any sign of BLA in the recall of numbers. In Experiment 3, a greater memory load task was given than that in Experiment 2, where two-digit numbers were presented successively (once, three and five times). Subjects were asked to recall the numbers. The results showed a significant BLA in the recall of numbers, i.e., the correct numbers in the correct temporal positions. These results strongly suggest that a benefit of redundant bilateral visual fields presentation is shown only in a highly cognitively demanding task, especially when it involves phonological memory loads.     

Lateralization of lexical codes in auditory word recognition

Three experiments examined the lateralization of lexical codes in auditory word recognition. In Experiment 1 a word rhyming with a binaurally presented cue word was detected faster when the cue and target were spelled similarly than when they were spelled differently. This orthography effect was larger when the target was presented to the right ear than when it was presented to the left ear. Experiment 2 replicated the interaction between ear of presentation and orthography effect when the cue and target were spoken in different voices. In Experiment 3, subjects made lexical decisions to pairs of stimuli presented to the left or the right ear. Lexical decision times and the amount of facilitation which obtained when the target stimuli were semantically related words did not differ as a function of ear of presentation. The results suggest that the semantic, phonological, and orthographic codes for a word are represented in each hemisphere; however, orthographic and phonological representations are integrated only in the left hemisphere.     

Rhyming and the right hemisphere

Subjects determined whether two successively presented and orthographically different words rhymed with each other. The first word was presented at fixation and the second was presented either to the left or to the right of fixation, either alone (unilateral presentation) or accompanied by a distractor word in the other visual hemifield (bilateral presentation). Subjects were more accurate when the words did not rhyme, when presentation was unilateral, and when the target was flashed to the right visual hemifield. It was predicted that bilateral presentation would produce interference when information from both visual fields was processed by one hemisphere (callosal relay), but not when each of the two hemispheres performed a task independently (direct access). That is, callosal relay tasks should show greater laterality effects with bilateral presentations, whereas direct access tasks should show similar laterality effects with both bilateral and unilateral presentations. Greater laterality effects were observed for bilaterally presented rhyming words, but nonrhyming words showed similar laterality effects for both bilateral and unilateral presentations. These results suggest that judgment of nonrhyming words can be performed by either hemisphere, but that judgment of rhyming words requires callosal relay to the left hemisphere. The absence of a visual field difference with nonrhyming word pairs suggests further that judgment of nonrhyming word pairs may be accomplished by the right hemisphere when presentation is to the left visual field.