Differences In Perceptual Processing Research Articles

Differences in early sensory-perceptual processing in synesthesia: A visual evoked potential study

Synesthesia is a condition where stimulation of a single sensory modality or processing stream elicits an idiosyncratic, yet reliable perception in one or more other modalities or streams. Various models have been proposed to explain synesthesia, which have in common aberrant cross-activation of one cortical area by another. This has been observed directly in cases of linguistic-color synesthesia as cross-activation of the ‘color area’, V4, by stimulation of the grapheme area. The underlying neural substrates that mediate cross-activations in synesthesia are not well understood, however. In addition, the overall integrity of the visual system has never been assessed and it is not known whether wider differences in sensory-perceptual processing are associated with the condition. To assess whether fundamental differences in perceptual processing exist in synesthesia, we utilised high-density 128-channel electroencephalography (EEG) to measure sensory-perceptual processing using stimuli that differentially bias activation of the magnocellular and parvocellular pathways of the visual system. High and low spatial frequency gratings and luminance-contrast squares were presented to 15 synesthetes and 15 controls. We report, for the first time, early sensory-perceptual differences in synesthetes relative to non-synesthete controls in response to simple stimuli that do not elicit synesthetic color experiences. The differences are manifested in the early sensory components of the visual evoked potential (VEP) to stimuli that bias both magnocellular and parvocellular responses, but are opposite in direction, suggesting a differential effect on these two pathways. We discuss our results with reference to widespread connectivity differences as a broader phenotype of synesthesia.

SEX DIFFERENCES IN PERCEPTUAL PROCESSING: PERFORMANCE ON THE COLOR-KANJI STROOP TASK OF VISUAL STIMULI

During color, colored Kanji characters and Stroop task of the visual stimuli, the P300 component of the event-related brain potential (ERPs) was used in conjunction with response time to identify sex differences in perceptual processing. Participants were instructed to respond to the display colors and name colored Kanji characters as quickly as possible in the respective stimulus conditions. Response time varied in all stimulus conditions, the males took longer than females. The P300 latency of males was longer and amplitude was smaller than females. The results suggest that cognitive strategy of males is different from females.

Perceptual and motor contributions to performance and ERP components after incorrect motor activation in a flanker reaction task

Objectives: The aims of this study are to evaluate contributions of response and perceptual processes to reaction performance in a flanker reaction task, and to investigate whether event-related potential (ERP) component N2 and error negativity N e represent similar or functionally distinct cortical mechanisms. Methods: ERPs, lateralized readiness potentials (LRPs) and reaction performance were measured in a flanker task with arrows as targets and congruent or incongruent flankers. Squares were used as neutral flankers. Target color signaled a response of the hand indicated by (PRO) or against (ANTI) the target arrow's pointing direction. Results: On both PRO and ANTI conditions, performance was facilitated by congruent and impaired by incongruent flankers. In the ERPs on trials with late response errors an N2 was evident before an N e. In addition, ERPs on correct trials showed an N2 particularly after incongruent flankers on PRO but for each flanker type on ANTI conditions. On incongruent ANTI trials, two successive response conflicts occurred but only a single N2 appeared. Conclusions: The results indicate that differences in perceptual processing contribute significantly to the flanker effects on task performance and provide further evidence that N2 and N e represent different cortical mechanisms. The data also suggest that N2 is not a real-time correlate of incorrect response suppression.

Perceptual and semantic sources of category-specific effects: event-related potentials during picture and word categorization.

In two experiments the effect of object category on event-related potentials (ERPs) was assessed while subjects performed superordinate categorizations with pictures and words referring to objects from natural (e.g., animal) and artifactual (e.g., tool) categories. First, a category probe was shown that was presented as name in Experiment 1 and as picture in Experiment 2. Thereafter, the target stimulus was displayed. In both experiments, analyses of the ERPs to the targets revealed effects of category at about 160 msec after target onset in the pictorial modality, which can be attributed to category-specific differences in perceptual processing. Later, between about 300-500 msec, natural and artifactual categories elicited similar ERP effects across target and category modalities. These findings suggest that perceptual as well as semantic sources contribute to category-specific effects. They support the view that semantic knowledge associated with different categories is represented in multiple subsystems that are similarly accessed by pictures and words.

Global/local processing in mentally retarded and nonretarded persons

This study examined intelligence-related differences in perceptual processing in a global/local task. Both mentally retarded and nonretarded persons processed global information faster than local information. Furthermore, both groups showed a similar global precedence effect. The effects of extensive practice at naming local features was also examined. Local processing times became faster for both groups as a result of local naming practice. The implication of the results are discussed in the context of global/local processing models as well as processing in other interference tasks (e.g., the Stroop task; Stroop, 1935). These results point to the need to assess task and processing parameters when extending findings of intelligence-related differences across apparently similar tasks.

Attentional and Perceptual Contributions to the Identification of Extrafoveal Stimuli: Adult Age Comparisons

Gerontological researchers have been cautioned that conclusions about age differences in attention may have been inferred from data that, in fact, reflected age differences in perceptual processing of stimuli falling outside the fovea (Cerella, 1985). Presumably, the experimental manipulations on which Cerella based his caution induced a broad focus of attention so that changes in perceptual processing would not be confounded with changes in attention. Experiment 1 tested this by comparing a condition similar to Cerella's with another in which attention was narrowly focused at fixation. The results replicated Cerella's findings. In addition, there were greater age differences when attention had been narrowly focused, showing that attentional effects can be separated from the effects reported by Cerella. Experiment 2 showed that age differences in extrafoveal perception could be removed by increasing the duration of the target from 200 to 2000 ms, suggesting that the perceptual deficits in older adults are due to differentially lengthened processing of stimuli outside the fovea.

On‐line measures of comprehension of natural and synthetic speech

Accumulated perceptual research comparing natural and synthetic speech indicates relatively large differences in tasks assessing acoustic‐phonetic processing, and small differences in tasks assessing higher levels of processing related to comprehension. Studies comparing comprehension of passages of fluent natural and synthetic speech have generally examined performance on questions presented after subjects have listened to a passage. Such postperceptual measures are known to be relatively insensitive to differences in “real‐time” processing operations. The present investigation employed an “on‐line” measure of processing, i.e., word monitoring, to study comprehension. Subjects in these studies were presented with three types of passages—(1) natural speech, (2) high‐quality synthetic speech, and (3) low‐quality synthetic speech—and were required to monitor for target words as well as verify postperceptual comprehension questions. Monitoring latencies and verification performance will be discussed in terms of differences in perceptual processing and comprehension of natural and synthetic speech. [Work supported by NSF.]

Temporal integration of form as a function of subject handedness and retinal locus of presentation

Two experiments are reported examining differences in perceptual processing as a function of subject handedness. Experiment 1 compared performance in the left vs right visual fields of right-vs left-handed subjects. Only right-handed subjects exhibited an interaction of visual field with spatial frequency (as mediated by interflash interval), suggesting that left-handers are not differentially lateralized for high vs low spatial frequency processing. Experiment 2 examined foveal performance in left-handers vs right-handers with or without familial sinistrality. Subjects with personal or familial sinistrality exhibited superior performance when the processing of low frequencies was required, suggesting that sinistrality may confer an advantage in the processing of lower spatial frequencies.

A Study of the Central Auditory Processes in Stutterers Using the Synthetic Sentence Identification (SSI) Test Battery

The performance of a group of stutters (N = 14) and a group of nonstutterers (N = 14) was compared on the Synthetic Sentence Identification Test (Speaks and Jerger, 1965). The test is designed to assess central auditory function. It was hypothesized that because of subtle neurologically based differences in perceptual processing, the performance of the two groups would differ significantly on one or more of the subtests. An analysis of variance revealed that the performance of the stuttering group was significantly poorer (0.01 level of confidence) than that of the nonstutteres on the Ipsilateral Competing Message Subtest. The results of the investigation were compatible with other studies that suggest a neurological dysfunction within the central auditory apparatus as at least one of the underlying causes of disfluency. It was concluded that further investigations of the central auditory processes in stutterers are warranted to make a more definitive statement about the etiology of stuttering.

Alternative processes in the identification of familiar pictures

Individual differences in perceptual processing were investigated in a task requiring subjects to match words (either general or specific category names) with simultaneously presented pictures. Based on the results of previous research, individual differences in processing were inferred from the effect, on "same" reaction time, of rotating the pictures into an unfamiliar orientation. For subjects inferred to emphasize an analytic mode of processing, word-picture matches were faster for general than for specific category names, supporting the hypothesis that analytic subjects would attend to the minimal number of features necessary to infer the categorical identity of the pictures. For subjects inferred to emphasize a structural mode of processing, there was little difference in word-picture matching time between specific and general category names, supporting the hypothesis that structural subjects would attend to all the information in the pictures, regardless of the category level specified by the word.

Comparison of Vowel and Consonant Perception

It has been suggested that there may be different mechanisms for vowel and consonant perception. A study of articulation-test-crew responses to minimal feature contrast vowel and consonant “rhyme” tests imbedded in various noises is reported here. Test-crew performance scores for vowels and consonants are compared with respect to noise spectral shape, test exposure, and specific test content by means of confusion matrices. Individual subject-response patterns for vowels and consonants are compared with respect to repeatability, predictability, variations from group means, and individual lingustic experience and history. It is found that perception of vowels relative to consonants varies among individuals, as does the absolute perception of each on a long-term average basis. This variation is not explicable in terms of individual pure-tone audiometric perception, or education, but may be related to individual linguistic experience and history as well as differences in perceptual processes. Occasional very large shifts in individual perception from trial to trial may be due to lapses in higher-order perceptual processes. No correlation was found between test scores and apparent subject fatigue to account for such lapses.