Hemispheric specialization for spatial frequency processing in the analysis of natural scenes

Experimental data coming from visual cognitive sciences suggest that visual analysis starts with a parallel extraction of different visual attributes at different scales/frequencies. Neuropsychological and functional imagery data have suggested that each hemisphere (at the level of temporo-parietal junctions-TPJ) could play a key role in spatial frequency processing: The right TPJ should predominantly be involved in low spatial frequency (LFs) analysis and the left TPJ in high spatial frequency (HFs) analysis. Nevertheless, this functional hypothesis had been inferred from data obtained when using the hierarchical form paradigm, without any explicit spatial frequency manipulation per se. The aims of this research are (i) to investigate, in healthy subjects, the hemispheric asymmetry hypothesis with an explicit manipulation of spatial frequencies of natural scenes and (ii) to examine whether the 'precedence effect' (the relative rapidity of LFs and HFs processing) depends on the visual field of scene presentation or not. For this purpose, participants were to identify either non-filtered or LFs and HFs filtered target scene displayed either in the left, central, or right visual field. Results showed a hemispheric specialization for spatial frequency processing and different 'precedence effects' depending on the visual field of presentation.     

Hemispheric specialization for categorical and coordinate spatial representations: A reappraisal

The purpose of the present study was to examine Kosslyn's (1987) claim that the left hemisphere (LH) is specialized for the computation of categorical spatial representations and that the right hemisphere (RH) is specialized for the computation of coordinate spatial representations. Categorical representations involve making judgements about the relative position of the components of a visual stimulus (e.g., whether one component is above/below another). Coordinate representations involve calibrating absolute distances between the components of a visual stimulus (e.g., whether one component is within 5 mm of another). Thirty-two male and 32 female undergraduates were administered two versions of a categorical or a coordinate task over three blocks of 36 trials. Within each block, items were presented to the right visual field-left hemisphere (RVF-LH), the left visual field-right hemisphere (LVF-RH), or a centralized position. Overall, results were more supportive of Kosslyn's assertions concerning the role played by the RH in the computation of spatial representations. Specifically, subjects displayed an LVF-RH advantage when performing both versions of the coordinate task. The LVF-RH advantage on the coordinate task, however, was confirmed to the first block of trials. Finally, it was found that males were more likely than females to display faster reaction times (RTs) on coordinate tasks, slower RTs on categorical tasks, and an LVF-RH advantage in computing coordinate tasks.     

Hemispheric specialization for reading

Behavioral laterality tasks with linguistic stimuli were used to assess the differential processing efficiencies of the cerebral hemispheres in right- and left-handed adults. Findings from a lateralized lexical decision task with concrete nouns supported Zaidel's (1983) "direct access" model of hemispheric functioning. A dual task consisting of oral and silent reading indicated that the right hand was significantly more disrupted than the left during unimanual finger tapping; however, some bilateral interference was observed. Taken together the findings suggest that although the left hemisphere was relatively more efficient, the right hemisphere was dynamically involved in the reading process.     

Acquisition of information from rapidly presented verbal and nonverbal stimuli

Two experiments tested recognition memory for rapidly presented stimuli. In Experiment I 16 words were presented at exposure times ranging from 25 to 500 msec followed by a yes-no recognition test. The results showed a strong dependence of memory performance on both exposure time and serial position. In Experiment II 16 random forms were presented at exposure times ranging from 125 to 2000 msec followed by a yes-no recognition test. Results for random forms showed that memory performance was strongly dependent on exposure time but not on serial position. Taken together, the results of Experiments I and II suggest qualitative encoding differences between verbal vs nonverbal stimuli.     

The language used in describing autobiographical memories prompted by life period visually presented verbal cues,event-specific visually presented verbal cues and short musical clips of popular music

Here, we examined linguistic differences in the reports of memories produced by three cueing methods. Two groups of young adults were cued visually either by words representing events or popular cultural phenomena that took place when they were 5, 10, or 16 years of age, or by words referencing a general lifetime period word cue directing them to that period in their life. A third group heard 30-second long musical clips of songs popular during the same three time periods. In each condition, participants typed a specific event memory evoked by the cue and these typed memories were subjected to analysis by the Linguistic Inquiry and Word Count (LIWC) program. Differences in the reports produced indicated that listening to music evoked memories embodied in motor-perceptual systems more so than memories evoked by our word-cueing conditions. Additionally, relative to music cues, lifetime period word cues produced memories with reliably more uses of personal pronouns, past tense terms, and negative emotions. The findings provide evidence for the embodiment of autobiographical memories, and how those differ when the cues emphasise different aspects of the encoded events.     

Hemispheric specialization for syntactic form

Pure nouns, verb-derived nouns, category-ambiguous words, and adjectives, all ending in -er, and matched for low and moderate-high frequency, were presented in each visual field to 24 normal, right-handed females. The four word classes were recognized at the same rate in the LVF, and at a significantly higher rate in the RVF. Contrary to earlier reports, there were no differences among pure nouns, verb-derived nouns, and category-ambiguous words, and effects appeared to be independent of word frequency. Neither hemisphere was demonstrated to give preferential access to the syntactic forms tested.     

Hemispheric specialization for emotional word processing is a function of SSRI responsiveness

Vulnerability to depression and non-response to Selective Serotonin Reuptake Inhibitors (SSRIs) are associated with specific neurophysiological characteristics including greater right hemisphere (RH) relative to left hemisphere (LH) activity. The present study investigated the relationship between hemispheric specialization and processing of emotional words using a divided visual field paradigm administered to never-depressed and previously-depressed individuals, who were subdivided into SSRI responders and non-responders. SSRI responders and never-depressed participants were similar in their left hemispheric lateralization for evaluating emotional words. In contrast, SSRI non-responders showed a relative shift towards RH processing of negative words, and a strong bias toward negative evaluation of words presented to the RH. The results are discussed within the context of a biological-cognitive model of vulnerability to depression.     

Hemispheric specialization for emotional word processing is a function of SSRI responsiveness

Vulnerability to depression and non-response to Selective Serotonin Reuptake Inhibitors (SSRIs) are associated with specific neurophysiological characteristics including greater right hemisphere (RH) relative to left hemisphere (LH) activity. The present study investigated the relationship between hemispheric specialization and processing of emotional words using a divided visual field paradigm administered to never-depressed and previously-depressed individuals, who were subdivided into SSRI responders and non-responders. SSRI responders and never-depressed participants were similar in their left hemispheric lateralization for evaluating emotional words. In contrast, SSRI non-responders showed a relative shift towards RH processing of negative words, and a strong bias toward negative evaluation of words presented to the RH. The results are discussed within the context of a biological–cognitive model of vulnerability to depression.     

Simultaneous processing of verbal and spatial information

Two experiments investigated the generality of the selective interference phenomenon by studying several different concurrent tasks, each involving either verbal or spatial information, and a range of retention intervals from 10 to 30 sec. The results supported the selective interference predictions, since the interference in performance was greater when the two simultaneous tasks both involved either verbal information or spatial information than when one of the tasks involved verbal and the other spatial information. It was concluded that not only was the selective interference phenomenon a rather general effect but that, since it was unaffected by changes in the nature of the component tasks, it was also probably caused by central processing capacity limitations rather than by competition for a specific structural mechanism.     

Hemispheric differences for verbal and nonverbal stimuli in Japanese- and English-speaking subjects assessed by Tsunoda's method

This investigation compared the performance of Japanese- and English-speaking subjects on T. Tsunoda's DAF key-tapping task, which he purports assesses cerebral dominance for language (1975, Brain and Language, 2, 152–170). Twenty-three native speakers of Japanese and 23 English-speaking subjects were employed in this study. Each subject was administered the DAF key-tapping task utilizing the vowel /a/ and a 1000-Hz pure tone. The results revealed an effect of intensity, whereby an increase in DAF/SAF ratios resulted in an increase in performance disruption. No differences were observed between the two language groups, ears, or between the 1000-Hz pure tone and the vowel /a/. Only 15.5% of the subjects showed the hypothesized right ear advantage for the tone when subjected to an analysis similar to Tsunoda's. All other subjects revealed variable degrees of advantage to either ear, to the same ear, or to to neither ear. It was concluded that no significant functional auditory asymmetry was observed for either group, suggesting that the DAF key-tapping task may not be a sensitive procedure to determine cerebral dominance for language among normals.     

Categorization versus distance: Hemispheric differences for processing spatial information

It has been hypothesized that the brain computes two different kinds of spatial-relation representations: one used to assign a spatial relation to a category and the other used to specify metric distance with precision. The present visual half-field experiment offers support for this distinction by showing that the left and right cerebral hemispheres make more effective use of the categorization and metric distance representations, respectively. Furthermore, the inclusion of a bilateral stimulus presentation condition permits the computation of a reversed association that offers additional support for the distinction between two types of spatial-relation representation.     

Short-term retention of visually presented stimuli: some evidence of visual encoding.

Subjects saw two visual stimuli on each trial, separated by an interval ranging from 0 to 8 sec. Each stimulus was composed of a subset of the dots of a 7 × 5 dot matrix. In particular, it was a composite of two patterns, one of which formed a capital English letter and the other of which was an arrangement formed by 8 randomly selected dots. The task was to decide as quickly as possible whether the two stimuli contained the same letter. Under one condition (correlated noise) the same noise pattern was used with both letters; thus the decision as to whether the letters were the same could be based on a test of congruence of the two stimuli, noise and all. Under another condition (uncorrelated noise) the noise patterns differed, assuring that the composite patterns differed, and thus precluding congruence testing as an adequate way to determine whether the two letters were the same. Performance was better (RTs and error rates were smaller) with the correlated noise than with the uncorrelated noise. The result was taken as evidence that visual information was retained in memory, and used to advantage, when the situation clearly warranted the direct comparison of visual patterns.     

Judgments of temporal duration while processing verbal and physiognomic stimuli

Left- and right-handed male college students made verbal estimations of temporal durations during performance of recognition memory for words and faces, and with no concurrent task. Time judgments were shorter with both concurrent memory tasks than in the control condition, but did not differ between the two memory tasks. Also, these results were additive across groups. Considering the differential involvement of the two cerebral hemispheres in processing verbal and physiognomic stimuli, and the lack of an interaction between group (left- vs right- handers) and memory task, it was concluded that the results do not support a lateralization of function hypothesis with respect to judgments of temporal duration.