Contrast of hand preferences between communicative gestures and non-communicative actions in baboons: Implications for the origins of hemispheric specialization for language

Gestural communication is a modality considered in the literature as a candidate for determining the ancestral prerequisites of the emergence of human language. As reported in captive chimpanzees and human children, a study in captive baboons revealed that a communicative gesture elicits stronger degree of right-hand bias than non-communicative actions. It remains unclear if it is the communicative nature of this manual behavior which induces such patterns of handedness. In the present study, we have measured hand use for two uninvestigated behaviors in a group of captive olive baboons: (1) a non-communicative self-touching behavior (“muzzle wipe” serving as a control behavior), (2) another communicative gesture (a ritualized “food beg”) different from the one previously studied in the literature (a species-specific threat gesture, namely “hand slap”) in the same population of baboons. The hand preferences for the “food beg” gestures revealed a trend toward right-handedness and significantly correlated with the hand preferences previously reported in the hand slap gesture within the same baboons. By contrast, the hand preferences for the self-touching behaviors did not reveal any trend of manual bias at a group-level nor correlation with the hand preferences of any communicative gestures. These findings provide additional support to the hypothesized existence in baboons of a specific communicative system involved in the production of communicative gestures that may tend to a left-hemispheric dominance and that may differ from the system involved in purely motor functions. The hypothetical implications of these collective results are discussed within the theoretical framework about the origins of hemispheric specialization for human language.     

Lateralized word recognition: assessing the role of hemispheric specialization, modes of lexical access, and perceptual asymmetry

The processing advantage for words in the right visual field (RVF) has often been assigned to parallel orthographic analysis by the left hemisphere and sequential by the right. The authors investigated this notion using the Reicher-Wheeler task to suppress influences of guesswork and an eye-tracker to ensure central fixation. RVF advantages obtained for all serial positions and identical U-shaped serial-position curves obtained for both visual fields (Experiments 1-4). These findings were not influenced by lexical constraint (Experiment 2) and were obtained with masked and nonmasked displays (Experiment 3). Moreover, words and nonwords produced similar serial-position effects in each field, but only RVF stimuli produced a word-nonword effect (Experiment 4). These findings support the notion that left-hemisphere function underlies the RVF advantage but not the notion that each hemisphere uses a different mode of orthographic analysis.     

Evolution of hemispheric specialization: advantages and disadvantages

Lateralization of the brain appeared early in evolution and many of its features appear to have been retained, possibly even in humans. We now have a considerable amount of information on the different forms of lateralization in a number of species, and the commonalities of these are discussed, but there has been relatively little investigation of the advantages of being lateralized. This article reports new findings on the differences between lateralized and nonlateralized chicks. The lateralized chicks were exposed to light for 24 h on day 19 of incubation, a treatment known to lead to lateralization of a number of visually guided responses, and the nonlateralized chicks were incubated in the dark. When they were feeding, the lateralized chicks were found to detect a stimulus resembling a raptor with shorter latency than nonlateralized chicks. This difference was not a nonspecific effect caused by the light-exposed chicks being more distressed by the stimulus. Instead, it appears to be a genuine advantage conferred by having a lateralized brain. It is suggested that having a lateralized brain allows dual attention to the tasks of feeding (right eye and left hemisphere) and vigilance for predators (left eye and right hemisphere). Nonlateralized chicks appear to perform these dual tasks less efficiently than lateralized ones. Reference is made to other species in discussing these results.     

Concurrent task interference in stutterers: dissociating hemispheric specialization and activation

Using all four combinations of hand and foot, adult stutterers and nonstutterers performed a unimanual sequential finger tapping task together with a stimulus-contingent foot responding task. The two groups were similar in that both demonstrated more dual-task interference when using the ipsilateral than contralateral limb pairs. Contrary to a prediction based on a hypothesis that attributes stuttering to neural interference due to an ungated or unregulated activity flow between the hemispheres, stutterers did not show more interference than nonstutterers when using the contralateral limb pairs. The groups did differ, however, in terms of finger tapping interference associated with right- versus left-foot concurrent task responding. Nonstutterers showed more interference when using the left than right foot. This was interpreted in terms of the attentional demands that the foot responding task placed on a system with an inherent left-hemisphere attentional bias. The lack of a reliable difference in stutterers with respect to interference by the two feet is consistent with indications from other research that stutterers have a relatively labile system of hemispheric attention or activation. The results of the study are placed into the context of a general model of the brain mechanisms associated with stuttering.     

Primary and secondard process in the context of cerebral hemispheric specialization

Increasing knowledge of human cerebral hemispheric specialization suggests a relationship between the different formal modes of thinking attributed to the two hemispheres and those psychoanalysis has traditionally assigned to primary (similar to recessive hemispheric) and secondary (similar to dominant hemispheric) processes. The fact of a lifelong capability at the neurophysiological level for coequal, simultaneous registration and organization of experience in these different cognitive modes allows primary process to be conceptualized in developmental terms. As the first organizing mode of infantile development, it shapes the primitive content of the dynamic unconscious. Thereafter, it can be viewed as coexistent and commingled with secondary process in dynamic tension, complementarity, and developing complexity. Observations from normal behavior, current research, and the functioning of the psychoanalyst support this thesis and reinforce an emerging viewpoint in contemporary psychoanalysis that primary processes are not confined to archaic levels but are open to growth and developmental integration into the complete range of ego functions.     

Dyslexic and typical-reading children use vowel digraphs as perceptual units in reading

Digraphs are graphemes that are composed of two letters like the "ou" in "soup". We hypothesized that the serial-reading strategy of dyslexic readers might interfere with the processing of digraphs. We used a letter-detection task to compare the processing of vowel digraphs in dyslexic and typical-reading children. Both groups were found to be slower in detecting a letter within a vowel digraph than in detecting a letter of a single-letter grapheme. The slower response to target letters embedded in a digraph was position independent in both groups. We also found that dyslexic children did not differ from typical-reading children in the detection of letters in words. These results indicate that typical-reading and dyslexic children process vowel digraphs as perceptual units and that dyslexic children do not show impairments in this early visual process.     

Dyslexic and typical-reading children use vowel digraphs as perceptual units in reading

Digraphs are graphemes that are composed of two letters like the “ou” in “soup”. We hypothesized that the serial-reading strategy of dyslexic readers might interfere with the processing of digraphs. We used a letter-detection task to compare the processing of vowel digraphs in dyslexic and typical-reading children. Both groups were found to be slower in detecting a letter within a vowel digraph than in detecting a letter of a single-letter grapheme. The slower response to target letters embedded in a digraph was position independent in both groups. We also found that dyslexic children did not differ from typical-reading children in the detection of letters in words. These results indicate that typical-reading and dyslexic children process vowel digraphs as perceptual units and that dyslexic children do not show impairments in this early visual process.     

Individual differences in the hemispheric specialization of dual route variables

The dual route model suggests that reading of letter strings can occur through both a lexical and a nonlexical route. Hemispheric specialization of these routes has also been posited, suggesting that the left hemisphere has both lexical and nonlexical routes while the right hemisphere has only a lexical route. However, some recent data conflict with this hemispheric dual route model, suggesting that both hemispheres may have access to both routes. The purpose of the present study was to investigate individual differences in the hemispheric specialization of these routes and to determine whether these group differences in their specialization might explain conflicts in the literature. The effect of four individual difference factors was explored: handedness, biological sex, menstrual stage (i.e., fluctuations in estrogen), and self-rated degree of masculinity (i.e., sexual attribution). We looked at the interaction of these individual differences with the following dual route variables: (i) string length, (ii) word frequency, (iii) regularity of grapheme-phoneme correspondences of words, and (iv) the interaction of frequency and regularity using a bilateral lexical decision task. We observed that sex, menstrual stage, and masculinity each affected hemispheric specialization of the dual route variables, but did so in different ways. We posit that both hemispheres have orthographical (lexical) access as well as phonological (nonlexical) access to words. Further, we suggest that the presence of phonological processing in the right hemisphere depends on available resources and the strategies used, which are subject to individual differences.     

Lateralized lexical decision in schizophrenia: hemispheric specialization and interhemispheric lexicality priming

Reports of left-hemisphere dysfunction and abnormal interhemispheric transfer in schizophrenia are mixed. The authors used a unified paradigm, the lateralized lexical decision task, to assess hemispheric specialization in word recognition, hemispheric error monitoring, and interhemispheric transfer in male, right-handed participants with schizophrenia (n=34) compared with controls (n=20). Overall, performance and error monitoring were worse in patients. However, patients like controls showed left-hemisphere superiority for lexical processing and right-hemisphere superiority for error monitoring. Only patients showed selective-interhemispheric lexicality priming for accuracy, in which performance improved when the lexical status of target and distractor stimuli presented to each hemifield was congruent. Results suggest that schizophrenia is associated with impaired monitoring and with increased interhemispheric automatic information transfer rather than with changed hemispheric specialization for language or error monitoring.     

Sex and handedness differences in EEG measures of hemispheric specialization

EEG alpha asymmetry was studied in 90 normal adults: right-handed, left-handed, and ambidextrous, male and female. Recordings were made from homologous central, parietal, and occipital leads, referenced to vertex, while subjects engaged in writing, speaking, reading, listening to speech, singing, and block design construction. These data confirm our previous findings that alpha asymmetry is task-dependent and extend them to a broader range of tasks, subjects, and leads. Among right-handers significant differences were found between the language tasks and the musical and spatial tasks: the $\text{R}\text{L}$ alpha ratio is higher in the language tasks. In addition, significant ordering of $\text{R}\text{L}$ alpha ratios was found among the language tasks themselves: WRITE å SPEAK > READ > LISTEN. No one “verbal” task can be considered representative of all language behaviors. Task differences in asymmetry were greater at the central than at the parietal leads, and no differences were found at the occiput. Differences among the handedness groups were found in $\text{R}\text{L}$ alpha ratio in specific tasks, in the relationship among tasks, and in alpha power level. Non-right-handers showed less task-dependent asymmetry. On some measures ambidexters appear to be a distinct group, not simply representing the middle range of a left-handed/right-handed continuum. Reversal of the “expected” right-handed pattern (SPEAK $\text{R}\text{L}$ ratio > BLOCKS $\text{R}\text{L}$ ratio) was seen in 10% of right-handers, and in 36% of left-handers, particularly among left-handed females (46%), suggesting a possible sex difference among non-right-handers. No sex difference was found among right-handers on any task with any measure at any lead.     

Acquired aphasia in children and the ontogenesis of hemispheric functional specialization.

We have described a series of 26 cases of cortical lesions in children from $\text{3}\text{1}\text{2}$ to 15 years of age (17 left-sided, six right-sided, three bilateral), in which 19 had varying degrees of language disturbance. We have attempted to establish the nature and evolution of these aphasic disorders, and have compared our observations to those previously published. Our analysis appears to indicate a relative hemispheric equipotentiality which permits the transfer of language representation to the opposite hemisphere in the case of a unilateral lesions in childhood. This conclusion, however, has at least the appearance of being in conflict with other reported findings, viz., those deriving from psychometric testing of subjects with unilateral perinatal lesions; and those concerning studies of fetal and newborn brains which suggest a very early, if not innate, hemispheric specialization.The fact of this discrepancy has lead us to reconsider the concept of a critical period as defined by Lenneberg. In this respect, we have also discussed the possibility of a partial transfer of language representation, of an intrahemispheric reorganization by intact “uncommitted” areas (P. Goldman), and finally, the need for an adequate stimulus during a given period in order for a preformed area to become functional.     

Right hemispheric specialization for mental imagery: A review of the evidence

An implicit assumption in the literature on functional hemispheric asymmetry is that the right hemisphere plays a special role in mental imagery. Using a definition of mental imagery as quasi-perceptual experience, we draw distinctions among visual imagery, visual recognition memory, and visuospatial abilities. We then review the research literature to evaluate the hypothesis that mental imagery is a specialized function of the right cerebral hemisphere, and find that it receives little unambiguous support. Case reports of loss of imagery are no more frequent with right than with left unilateral brain damage. Systematic studies of brain-injured patients provide some support for the hypothesis, but are also consistent with the alternative hypothesis of bilateral representation of imagery. Commissurotomized patients report dreaming and being able to form visual images. Behavioral and psychophysiological studies of non-brain-injured patients either fail to provide evidence in favor of the hypothesis or can be interpreted as compatible with the alternate hypothesis of bilateral hemispheric involvement in imagery. We conclude that there is, presently, insufficient empirical basis for considering imagery a right hemispheric function. We then discuss implications of this conclusion for future research.     

Strategy use in the reading span test: an analysis of eye movements and reported encoding strategies

Strategy use in the traditional reading span test was examined by recording participants' eye movements during the task (Experiment 1) and by interviewing participants about their strategy use (Experiment 2). In Experiment 1, no differences between individuals with a low, medium, and high span were observed in how they distributed processing time between task elements. In all three groups, fixation times on words up to the to-be-remembered (TBR) word became shorter and the time spent on the TBR longer as memory load in the task increased. The results of Experiment 2, however, show that span groups differ in the use of memory encoding strategies: individuals with a low span use mainly rehearsal, whereas individuals with a high span use almost exclusively semantic elaboration. The results indicate that the use of elaborative strategies may enhance span performance but that not all individuals are necessarily able to use such strategies efficiently.     

Change detection in complex scenes: hemispheric contribution and the role of perceptual and semantic factors

The perceptual salience and semantic relevance of objects for the meaning of a scene were evaluated with multiple criteria and then manipulated in a change-detection experiment that used an original combination of one-shot and tachistoscopic divided-visual-field paradigms to study behavioural hemispheric asymmetry. Coloured drawings that depicted meaningful situations were presented centrally and very briefly (120 ms) and only the changes were lateralised by adding an object in the right or in the left visual hemifield. High salience and high relevance improved both response times (RTs) and accuracy, although the overall contribution of salience was greater than that of relevance. Moreover, only for low-salience changes did relevance affect speed. RTs were shorter when a change occurred in the left visual hemifield, suggesting a right-hemisphere advantage for detection of visual change. Also, men responded faster than women. The theoretical and methodological implications are discussed.     

Sentential structure and the perceptual span in normal reading development

An eye-voice span paradigm was adopted to determine whether children use different aspects of sentence structure to facilitate decoding early in the course of reading development. Eightyfour Grade 1 and Grade 2 children, representing four levels of early reading competence, and 15 skilled adult subjects read from four textual conditions; materials varied in the extent to which the texts were semantically and/or syntactically constrained. The more precocious the young reader, the longer his reported span. The better readers' and the adults' advantage was greater the more linguistically constrained the reading material. These data support a continuous model fo reading development and are compatible with an interactive definition of early reading behavior.     

Vertical perceptual span and the processing of visual signals in reading

A previous study by Pollatsek et al. ( 1993 ) claims that the perceptual span in reading is restricted to the fixated line, i.e. readers typically focus their visual attention on the line of text being read. The present study investigated whether readers make use of content structure signals (paragraph indentations and topic headings) present several lines away from the currently fixated line. We reasoned that as these signals are low-resolution visual objects (as opposed to letter and word identity), readers may attend to them even if they are located some distance away from the fixated line. Participants read a hierarchically organized multi-topic expository text containing structure signals in either a normal condition or a window condition, where the text disappeared above and below a vertical 3° gaze-contingent region. After reading, participants were asked to produce a written recall of the text. The results showed that the overall reading rate was not affected by the window. Nevertheless, the headings were reread more in the normal condition than in the window one. In addition, more topics were recalled in the normal than in the window condition. We interpret the results as indicating that the readers visually attend to useful text layout features while considering bigger units than single text lines. The perception of topic headings located away from the fixated line may favour long-range regressions towards them, which in turn may favour text comprehension. This claim is consistent with previous studies that showed that look-back fixations to headings are performed with an integrative intent.     

Eye movements and the perceptual span in silent and oral reading

Previous research has examined parafoveal processing during silent reading, but little is known about the role of these processes in oral reading. Given that masking parafoveal information slows down silent reading, we asked whether a similar effect also occurs in oral reading. To investigate the role of parafoveal processing in silent and oral reading, we manipulated the parafoveal information available to readers by changing the size of a gaze-contingent moving window. Participants read silently and orally in a one-word window and a three-word window condition as we monitored their eye movements. The lack of parafoveal information slowed reading speed in both oral and silent reading. However, the effects of parafoveal information were larger in silent reading than in oral reading, because of different effects of preview information on both when the eyes move and how often. Parafoveal information benefitted silent reading for faster readers more than for slower readers.     

Resource allocation and the attentional demands of letter encoding

The idea that familiar events can be encoded automatically has gained general acceptance in cognitive psychology since Posner and Boies (1971) first reported that reaction times to a secondary probe were not interfered with by letter encoding. More recently, Ogden, Martin, and Paap (1981) used a more valid control for estimating baseline probe performance and found secondary task interference, suggesting that letter encoding does require attentional resources. The present series of experiments began with the aim of evaluating Ogden et al's evidence against automaticity when the first letter was not terminated after a brief exposure, as was done in their study. In the first set of experiments we found evidence of encoding interference when the interval between the two letters was varied (50 to 1,000 msec), but this interference disappeared when there was a constant 1,000-msec interval between the letters. On the basis of these findings, we hypothesized that changes in the primary task (e.g., the exposure duration of the first letter or the interval between the two letters) may influence the momentary allocation of resources between the primary and secondary tasks. More specifically, we hypothesized that any momentary reduction in the resources demanded by the primary tasks results in a reallocation of resources to the secondary task, which in turn reduces the sensitivity of the secondary task to the demands of the primary task, that is, probe performance is moved into the data-limited region of processing (Norman & Bobrow, 1975). This idea was tested by reducing resource allocation to the probe task at the time of encoding by reducing the expectancy (i.e., the probability) of probes in the temporal proximity of the first letter. The results showed that this manipulation produced a large and significant increase in encoding interference. Moreover, when the intensity of the tone (probe) was decreased from 70 to 60 dB, the magnitude of encoding interference was further increased. In regard to the specific issue of automaticity, the findings suggest that encoding familiar events does require resources, which will result in secondary task interference given that the secondary task is in the resource-limited region of processing. More important, the findings suggest that the magnitude of secondary task interference is dependent on within-trial changes in resource allocation between the primary and secondary tasks. This possibility has general implications for dual-task methodology and the measurement of attentional demands.