图形同一性对视觉似动的影响

该研究以单字母为刺激材料考察了图形同一性对视觉似动的影响。按照图形同一性、字母顺序及图形位移方向的不同,字母图形分成４类。另外还比较了聚焦和不聚焦条件下的实验结果。实验中要求被试对字母作左向、右向或来回运动的判断。结果表明似动现象不仅受到刺激间的空间关系的影响,而且也受到刺激间的图形同一性的影响。     

Effect of compatibility of S-R mapping on reactions toward the stimulus source

This research was concerned with separating the effects of three varieties of S-R compatibility: reactions toward the stimulus source, compatibility of S-R mapping, and display-control arrangement correspondence. In experiments 1 and 2, subjects pressed a green or red key located on the left and right in response to the onset of a green or red stimulus presented in a left or right window. Half of the subjects pressed the key which corresponded to the color of the stimulus (compatible S-R mapping) while the other half pressed the alternate colored key (incompatible S-R mapping). In the compatible mapping task, reactions were faster when location of stimulus and response corresponded than when they did not while, in the incompatible task, reactions were faster when location of stimulus and response did not correspond. This apparent reversal in the tendency to react toward the stimulus source was attributed to display- control arrangement correspondence rather than to logical recoding of the directional cue. Experiment 3 established that faster reactions toward the stimulus source occured only under compatible mapping instructions.     

Asynchrony of lateral onset as a factor in difference in visual field.

An experiment in matching judgments was designed to examine a role of perceptual process in apparent asymmetry. Recognition of Hirakana letters (Japanese letters) was required. The experimental condition in which stimuli were presented to the left visual field first and to the right visual field second produced more errors for all stimulus intervals (0 to 60 msec.) than experimental conditions where stimuli were presented to the right visual field first and to the left one second. Especially, superiority of the latter condition was marked with the longest stimulus interval employed. These results indicate superiority of the left hemisphere function for recognizing Hirakana letters and suggest that not only memory but also perceptual process contributes to this laterality effect.     

Lateral masking as a determinant of global dominance.

The term compound letter refers to a large (global) letter made up of small (local) letters. Reaction time to identify local letters is longer when local and global letters are different than when they are the same (the global dominance effect). The possible contribution of lateral masking to this effect was investigated. Lateral masking denotes reduced probability of identifying a stimulus when it is closely surrounded by other stimuli (as is the case for the local items in a compound stimulus). Three experiments were conducted in which the dependent measure was percentage of correct responses, rather than reaction time. In experiment 1 compound letters were used; accuracy of performance yielded evidence of global dominance such as obtained with reaction time measures. In experiments 2 and 3 the strength of lateral masking in geometrical forms was varied by varying the density of their component items. In agreement with earlier suggestions based on indirect evidence, the results directly implicated lateral masking as an important determinant of global dominance. However, lateral masking could not account fully for the experimental outcome. Factors beyond lateral masking, such as global precedence in the processing sequence or inhibitory interactions among low and high spatial-frequency components of the compound images are required in order to provide a comprehensive account of global dominance effects.     

Laterality differences and practice effects under central backward masking conditions

Two experiments were conducted to examine laterality differences and practice effects under various central backward masking conditions. Critical stimulus onset asynchrony (SOA) was determined for subjects on 3 consecutive days using single letters as target stimuli (TS) and a pattern masking stimulus (MS). There was a right visual field (RVF) advantage on Day 1 but no difference between the visual fields on following days. The decline in the RVF advantage appeared to be dependent upon prior experience with laterally located letters, to be independent of initial experience with a particular set of letters, and to be more pronounced for females than for males. In addition, large improvements in performance were found, particularly between the first and second testing sessions. These practice effects were discussed in terms of the possible development of strategies for enhancing TS features or attenuating MS features.     

Evaluating a split processing model of visual word recognition: effects of orthographic neighborhood size

The split fovea theory proposes that visual word recognition of centrally presented words is mediated by the splitting of the foveal image, with letters to the left of fixation being projected to the right hemisphere (RH) and letters to the right of fixation being projected to the left hemisphere (LH). Two lexical decision experiments aimed to elucidate word recognition processes under the split fovea theory are described. The first experiment showed that when words were presented centrally, such that the initial letters were in the left visual field (LVF/RH), there were effects of orthographic neighborhood, i.e., there were faster responses to words with high rather than low orthographic neighborhoods for the initial letters ('lead neighbors'). This effect was limited to lead-neighbors but not end-neighbors (orthographic neighbors sharing the same final letters). When the same words were fully presented in the LVF/RH or right visual field (RVF/LH, Experiment 2), there was no effect of orthographic neighborhood size. We argue that the lack of an effect in Experiment 2 was due to exposure to all of the letters of the words, the words being matched for overall orthographic neighborhood count and the sub-parts no longer having a unique effect. We concluded that the orthographic activation found in Experiment 1 occurred because the initial letters of centrally presented words were projected to the RH. The results support the split fovea theory, where the RH has primacy in representing lead neighbors of a written word.     

Hemispheric patterns in visual search

A visual search paradigm was employed to examine hemispheric serial and parallel processing. Stimulus arrays containing 4, 9, or 16 elements were tachistoscopically presented to the right visual field-left hemisphere (RVF-LH) or left visual field-right hemisphere (LVF-RH). Subjects judged whether all of the elements within an array were physically the same (all X's) or whether one (O) was different from the rest. Left hemisphere presentations were processed more quickly and accurately than LVF-RH presentations for all stimulus conditions. As the number of array elements increased, more errors and longer response times were obtained for different stimulus items whereas fewer errors and somewhat shorter response times were obtained for same stimulus items. These and previous results suggest that the left hemisphere obtains an advantage for visual search because of that hemisphere's superiority for fine-grained feature analysis rather than because of a fundamental hemispheric serial/parallel processing dichotomy.     

Development of differences in response latencies to right and left visual fields

Robust lateralization developed in right-handed adults who were asked to judge letter pairs as "same" or "different" during 4608 trials. By the end of the first two blocks (768 trials) "same" responses were favored when presented in the RVF (transmitted directly to the left hemisphere) and "different" responses were favored when presented in the LVF (transmitted direction to the right hemisphere). This gradually reversed over sessions with "same" responses becoming faster for letters presented in the LVF, and "different" responses becoming faster for stimuli presented in the RVF. The laterality acquired under these conditions was cumulative and reproducible, appeared in all 16 subjects, and was preserved between sessions a week apart. The data suggest that laterality is a flexible and reversible characteristic of the human brain even when stimulus and task remain constant.     

Vocal and manual response latencies to bilateral and unilateral tachistoscopic letter displays

Bilateral rows of eight letters and unilateral rows of four letters were presented in randomized sequences for 100 ms. Subjects were required to recall all letters in a trial (Experiment I); recall letters from one hemifield cued at exposure (Experiment II); recognize a single letter, making a vocal response (Experiment III); recognize a single letter, making a manual response (Experiment IV). In Experiments I, II and III, identification errors were fewer and vocal response latencies were faster for RVF stimuli, except in the bilateral condition on Experiment I; in Experiment IV manual response latencies were the same, for left and right, bilateral and unilateral conditions. Collectively, the results could not be satisfactorily accounted for by any one hypothesis: report-order, trace-scanning, or cerebral dominance. The relative contribution of each process to the laterality effect was discussed.     

Evidence for an addition to the reading scan hypothesis

Letters were tachistoscopically presented in pairs to the left or right of fixation for 40 msec. The pair consisted of a target letter (B, D, P, or T) and a noise letter (all other letters of the alphabet except I), with the noise letter appearing either to the inside or the outside of the stimulus letter. S’s task was to report verbally the target letter as fast as possible. Reaction times and number of errors indicated that there was more interference when the noise letter occurred further from the fixation point than the target letter for both the left and right visual field. Since a reading scan cannot account for the results in the right visual field, an outside-toward-fixation scan is proposed. An analysis of the different kinds of errors indicated that the outside to fixation scan is more primitive than the reading scan in that it produces less detailed information about the letters than does the reading scan.     

Differential specialization of the cerebral hemispheres for the perception of sameness and difference

The Johns Hopkins University, Baltimore, Maryland 21218 Pairs of letters were presented 4 deg left or right of fixation, and Ss were asked to indicate as quickly as possible whether the letters in a pair were the same or different. Reaction times for “different” responses were faster when stimuli were in the left visual field than in the right, but reaction times for “same” responses were faster when stimuli were in the right visual field than in the left. These results may indicate that the right hemisphere is better specialized for difference detection, while the left hemisphere is better specialized for sameness detection.     

Hemispheric differences in processing handwritten cursive

Hemispheric asymmetry was examined for native English speakers identifying consonant-vowel-consonant (CVC) non-words presented in standard printed form, in standard handwritten cursive form or in handwritten cursive with the letters separated by small gaps. For all three conditions, fewer errors occurred when stimuli were presented to the right visual field/left hemisphere (RVF/LH) than to the left visual field/right hemisphere (LVF/RH) and qualitative error patterns indicated that the last letter was missed more often than the first letter on LVF/RH trials but not on RVF/LH trials. Despite this overall similarity, the RVF/LH advantage was smaller for both types of cursive stimuli than for printed stimuli. In addition, the difference between first-letter and last-letter errors was smaller for handwritten cursive than for printed text, especially on LVF/RH trials. These results suggest a greater contribution of the right hemisphere to the identification of handwritten cursive, which is likely related visual complexity and to qualitative differences in the processing of cursive versus print.     

Hemispheric memory for random forms revisited

Hemispheric short-term memory was studied by projecting complex random forms that varied in their verbal association strength to the left and right hemispheres. Male and female subjects responded same or different to a centrally presented memory test stimulus which occurred 0, 5, 10, or 20 sec after the target item. Reaction time for both response judgments was significantly shorter for right-hemisphere presentations over all memory intervals. For both performance measures, response judgment interacted with the length of memory interval and the verbal association value of the stimulus items. No hemispheric differences were observed as a function of subject sex. Hemispheric memory for complex forms appears primarily dependent upon task processing demands rather than stimulus factors when response time is used to measure recognition under tightly controlled conditions.     

Selective attention and target search with brief visual displays

In a series of four experiments, subjects were presented with eight item arrays tachistoscopically. In two tasks, the subject was required to recall a digit presented among seven letters or a letter among seven digits. The remaining tasks required the subject to detect the presence of a specific letter either in the context of seven random letters or seven digits. An examination of the effects of a masking stimulus for various target positions suggested that subjects could attend selectively when the target was a different category than its context but had to process the entire array when the target was the same category as the context. The effects of selective attention and masking are explained in terms of parallel and sequential identification processes.     

A left hemisphere, but not right hemispace, advantage for tactual simultaneity judgments

Hemispheric asymmetries for tactile simultaneity judgments were investigated in 34 dextral adults. Pairs of vibrotactile stimuli with simultaneous or successive onsets were delivered unilaterally to the left or right hand. Participants made a forced-choice, bipedal response, indicating whether a stimulus was simultaneous or successive. The effect of hemispatial attentional biases was investigated, using ipsilateral (arms uncrossed) and contralateral (arms crossed) hand placements. Trials presented to the right hand were associated with fewer errors and a trend for faster response times than were those presented to the left hand. There was no asymmetry in response bias. Manipulations of hemispace did not affect the right hand advantage. These results confirm the existence of a left hemisphere temporal-processing advantage but fail to demonstrate that the asymmetry is the result of a rightward attentional bias. The implications of these results for absolute and relative models of hemispheric specialization are discussed.     

Synchronization error in bilateral simultaneous flexion of elbows.

Using 7 left- and 7 right-handed subjects, the difference in time between left and right arms in the initiation of bilateral simultaneous flexion of elbows (synchronization error) was measured under three conditions: response to a sound stimulus with a warning signal, response to a sound stimulus without a warning signal, and self-initiated trial (option). The absolute value of synchronization errors depended upon experimental conditions. In conditions 'with warning' and 'option' the dominance shown in performance of left-handed subjects was the mirror-image of that shown by the right-handed subjects. The right biceps muscle responded faster in left-handed subjects and vice versa. Right-handed subjects showed rather a constant value in their dispersion of synchronization errors.     

Separating effects of orthographic similarity and contour summation in the identification of masked letter strings

We separated effects of contour summation and orthographic similarity under masking conditions, by comparing identification with simultaneous and sequentially presented letter strings, which either did or did not overlap spatially. With overlapping simultaneous stimuli, performance was better for strings with similar contours than for strings with the same letters (the orthographic similarity condition). This suggests that contour summation effects were strongest in the condition where stimuli had similar contours. With sequential presentations, performance in the similar contour and the orthographically similar conditions was equated when the stimuli were overlapping. However, effects of contour summation decreased when prime and target letters were spatially displaced, whereas performance in the orthographically similar condition was maintained. We conclude that effects of orthographic similarity can be distinguished from effects of contour summation, under masking conditions.     

Stimulus intensity, attentional instructions, and the ear advantage during dichotic listening

The present experiment was designed to investigate the effects of the following two variables on the identification of dichotically presented CV syllables: (1) the relative difference in intensity levels of the stimuli presented to the two ears and (2) the instructions to attend to both ears or to focus attention on one ear. As expected for a verbal task, more CV's were identified from the right ear than from the left ear. Furthermore, identification of stimuli presented to one ear improved when (1) those stimuli were relatively higher in volume than the stimuli presented to the other ear and (2) when subjects were instructed to focus attention on only that ear rather than distribute attention across both ears. Of particular importance is the finding that the effects of relative stimulus intensity are the same under conditions of focused attention as under conditions of divided attention. This finding is inconsistent with an attention explantation of the relative intensity effects. Instead, the results are consistent with a model of dichotic listening in which ear of stimulus presentation and relative stimulus intensity influence a perceptual stage of information processing and attentional instructions influence a subsequent response selection stage.     

Functionally lateralised information processing and its allocation to response: Inferences from three measures of letter identification performance following lateralised visual input

Identification errors were analysed for single letters presented in each visual hemi-field. The kinds of errors occurring reflected both how the letters were made difficult to see, and the informational relationships among the possible stimulus letters. The particular pattern of errors was different in the two hemifields, with the direction of that difference suggesting the letters were better differentiated following left half-brain input. But this left-sided superiority in letter differentiation was only sometimes reflected in faster or more accurate responses overall. Instead, the extent of left-sided performance superiority in RT and accuracy depended in a complex way on the degree of difficulty of the task. This influence of task difficulty on the RT and accuracy measures of functional laterality was considered to reflect a greater or lesser allocation to response of the lateralised letter-differentiation process revealed by the errors analysis.     

Temporal aspects of selective masking

In two experiments, rows of random letter sequences were presented for 100 ms and were patterned masked at varying delays after display offset. In Experiment I recall was probed by visual partial report cues, while auditory probes were employed in Experiment II. Compared to no-masking control conditions, the masking stimulus had a selective effect at the different positions of the rows. The masking stimulus produced the largest decrements in recall of letters from the centre positions of the displays but had a minimal effect on performance at either end of the rows. Furthermore, it was demonstrated that improvements in recall were limited to the centre positions of the rows at increased delays of mask. Subsidiary analyses revealed that processing of the end letters of the displays terminates shortly after display offset while processing of the centre letters continues for at least 500 ms. The results are consistent with the notion that processing of multi-letter arrays commences at the ends of the rows and that the selective masking effect reflects the order of processing of the contents of iconic memory. However, these results were evident only in Experiment II which employed auditory partial report cues. When the partial report cues were visual, there were no effects of masking and minimal increases in performance at increased delays of mask. The discrepant results of the two experiments are discussed in terms of process interruption caused by obligatory attention to the partial report cues.