Hemispheric emotional asymmetry in a dichotic listening task.

In a dichotic listening experiment white noise was played to one ear and either music or poetry to the other ear. Subjects rated the stimuli on each of three dimensions. The results showed that both music poetry were judged as more pleasant when heard at the left than the right ear. In addition the music, but not the poetry, was perceived as more soothing at the left ear. The findings are discussed in relation to other indications in the literature that left and right cerebral hemispheres differ in their emotional make-up.     

Ear asymmetry in perception of emotional non-verbal stimuli

Hemispheric asymmetry for perception of non-verbal emotional human voices was investigated in normal subjects by dichotic listening utilizing non-verbal responses. As in former experiments, a slight but significant left ear superiority was found. This finding suggests that mediation of these stimuli is done by the right hemisphere. The dominant role of the right hemisphere in this perceptual task is discussed in terms of an earlier development of this hemisphere.     

Hemispheric asymmetry for linguistic prosody: a study of stress perception in Croatian

The aim of the study was to test for possible functional cerebral asymmetry in processing one segment of linguistic prosody, namely word stress, in Croatian. The test material consisted of eight tokens of the word pas under a falling accent, varying only in vowel duration between 119 and 185 ms, attached to the end of a frame sentence. The sentence could, depending on the duration of the vowel, mean 'This is a beautiful dog' or 'This is a beautiful belt/waist.' Each sentence was presented eight times in three dichotic listening conditions (binaural, left ear only, right ear only), in random order. Fourty healthy female right-handers participated in a forced-choice lexical task. For each presented sentence they had to decide whether it referred to the animal (short vowel in the key word) or to the belt/waist (long vowel in the key word). Their oral responses were analyzed in terms of response time and categoricity. No consistent significant differences were found among listening conditions. The responses possibly reflect the nonlateralized activity of subcortical regions or a simultaneous activity of both hemispheres relying on different cues.     

Hemispheric specialization for the perception of speech sounds: The influence of intonation and structure

The present report investigates the effect of various cues to phrase structure upon the hemispherically lateralized processing of phonetic structure. Meaningless sequences were paired for dichotic presentation and were delivered under two different conditions termed structured and semistructured. The dichotic sequences in the two conditions contained the same nonsense syllable stems, English bound morphemes, and English function words. Also each of the sequences in both conditions were grammatically ordered in the sense that if the nonsense stems were replaced by English stems, a grammatical sentence would result. The conditions differed with respect to prosody, however: the structured sequences were characterized by the acoustic correlates of constituent structure; the semistructured sequences were delivered in a monotone. A significant right-ear superiority was observed in the structured condition, but not in the semistructured condition. These perceptual laterality differences are discussed in relation to cerebral dominance for language and in relation to speech processing generally.     

Hemispheric asymmetry in the efficiency of attentional networks

Despite the fact that hemispheric asymmetry of attention has been widely studied, a clear picture of this complex phenomenon is still lacking. The aim of the present study was to provide an efficient and reliable measurement of potential hemispheric asymmetries of three attentional networks, i.e. alerting, orienting and executive attention. Participants (N=125) were tested with the Lateralized Attention Network Test (LANT) that allowed us to investigate the efficiency of the networks in both visual fields (VF). We found a LVF advantage when a target occurred in an unattended location, which seems to reflect right hemisphere superiority in control of the reorienting of attention. Furthermore, a LVF advantage in conflict resolution was observed, which may indicate hemispheric asymmetry of the executive network. No VF effect for alerting was found. The results, consistent with the common notion of general right hemisphere dominance for attention, provide a more detailed account of hemispheric asymmetries of the attentional networks than previous studies using the LANT task.     

Hemispheric asymmetry in cross-race face recognition

This study examines two phenomena related to face perception, both of which depend on experience and holistic processing: perceivers process faces more efficiently in the right hemisphere of the brain (a hemispheric asymmetry), and they typically show greater recognition accuracy for members of their racial ingroup (a cross-race recognition deficit). The current study tests the possibility that these two effects are related. If asymmetry depends on experience, it should be particularly evident with (more familiar) ingroup faces; if cross-race recognition relies on holistic processing, it should be particularly evident for faces presented to the right hemisphere. Black and White participants viewed Black and White faces presented to either the left or right visual field. As predicted, participants showed a more pronounced asymmetry for ingroup (rather than outgroup) faces, and cross-race recognition deficits were more pronounced for stimuli presented to the left (rather than the right) visual field.     

Hemispheric sensitivity differences in the perception of colour

Signal detection analysis was performed on data obtained from discrimination tasks using lateralized coloured stimuli. It was found that there was a right hemisphere superiority in discriminability to both hue and saturation.     

Hemispheric differences for feature perception

Summary Hemisphere differences for featural processing were investigated in three experiments. Stimulus arrays composed of the same background letter were presented tachistoscopically and the subject instructed to detect an embedded target letter. Background and target letter features were manipulated across studies, while stimulus arrays were presented at different retinal loci within experiments. Signal detection analysis revealed that left hemisphere stimulus presentations demonstrated slightly better detection when target and background features were relatively dissimilar, while right hemisphere stimulus presentations demonstrated better detection when target and background features were highly similar. Retinal locus generally decreased detection performance when the stimulus letters were dissimilar and interacted with hemispheric advantages. Both of these factors also were affected by changes in response criterion across experiments which were linked to target/background perceptual confusions. The findings suggest that the left and right hemispheres differ in their feature extraction capabilities during the early stages of visual stimulus processing.     

The effect of congenital deafness on cerebral asymmetry in the perception of emotional and non-emotional faces.

Functional hemispheric specialization in recognizing faces expressing emotions was investigated in 18 normal hearing and 18 congenitally deaf children aged 13-14 years. Three kinds of faces were presented: happy, to express positive emotions, sad, to express negative emotions, and neutral. The subjects' task was to recognize the test face exposed for 20 msec in the left or right visual field. The subjects answered by pointing at the exposed stimulus on the response card that contained three different faces. The errors committed in expositions of faces in the left and right visual field were analyzed. In the control group the right hemisphere dominated in case of sad and neutral faces. There were no significant differences in recognition of happy faces. The differentiated hemispheric organization pattern in normal hearing persons supports the hypothesis of different processing of positive and negative emotions expressed by faces. The observed hemispheric asymmetry was a result of two factors: (1) processing of faces as complex patterns requiring visuo-spatial analysis, and (2) processing of emotions contained in them. Functional hemispheric asymmetry was not observed in the group of deaf children for any kind of emotion expressed in the presented faces. The results suggest that lack of auditory experience influences the organization of functional hemispheric specialization. It can be supposed that in deaf children, the analysis of information contained in emotional faces takes place in both hemispheres.     

Hemispheric asymmetry reduction in older adults: the HAROLD model

A model of the effects of aging on brain activity during cognitive performance is introduced. The model is called HAROLD (hemispheric asymmetry reduction in older adults), and it states that, under similar circumstances, prefrontal activity during cognitive performances tends to be less lateralized in older adults than in younger adults. The model is supported by functional neuroimaging and other evidence in the domains of episodic memory, semantic memory, working memory, perception, and inhibitory control. Age-related hemispheric asymmetry reductions may have a compensatory function or they may reflect a dedifferentiation process. They may have a cognitive or neural origin, and they may reflect regional or network mechanisms. The HAROLD model is a cognitive neuroscience model that integrates ideas and findings from psychology and neuroscience of aging.     

Hemispheric asymmetry in temporal resolution: Contribution of the magnocellular pathway

Right-handed participants performed simple visual judgments on nonverbal stimuli presented either to the left visual field-right hemisphere (LVF-RH) or to the right visual field-left hemisphere (RVF-LH). The stimuli were exposed for 40-120 msec, followed by a backward mask. When the stimuli were presented against a green background, an RVF-LH advantage was observed for the shortest exposure duration. This result supports the notion that the LH has finer temporal resolution than the RH. Imposition of a red background disrupted performance and eliminated the RVF-LH advantage for the shortest exposure duration. Because the red background attenuates functions of the magnocellular pathway, these results suggest that the magnocellular pathway contributes to the LH advantage for fine temporal resolution.     

Cerebral asymmetry in time perception

Eighteen right-handed male subjects estimated the duration of dot patterns of varying numerosity which were briefly flashed to the left and right visual fields. The mean judged duration of patterns flashed to the left visual field was significantly less than the mean judged duration of patterns flashed to the right visual field. However, the duration of all patterns was underestimated, regardless of visual field. In addition, apparent duration increased linearly when plotted as a function of log duration and increased monotonically when plotted as a function of stimulus numerosity. Overall accuracy was nearly equivalent in both visual fields, but there were interactions between actual durations and visual field and between numerosity and visual field. Thomas and Weaver’s [1975) model for time perception is applied to the data, and it is suggested that the left hemisphere relies on a timer to estimate duration, while the right hemisphere relies on a visual information processor to estimate duration. nt]mis|The author would like to thank A. B. Kristofferson, S. F. Witelson, an anonymous referee, Mary Kay Fortman, and Allen Gouse for their helpful comments. Some of these data were presented at the meeting of the Midwestern Psychological     

Ear asymmetry in reaction time to musical sounds

Dichotic pairs of musical sounds were presented to 16 right-handed subjects, who were instructed to depress a reaction-time (RT) button when a target sound occurred in either ear. Four blocks of 36 trials were presented. During the first block, RTs to left-ear targets were significantly faster than those to right-ear targets. There were no significant ear differences during the second, third, or fourth blocks. Possible explanations for the limited duration of the left-ear advantage, and its implications for models proposed to explain the basis of RT asymmetries, are discussed.     

Hemispheric differences in the effects of context on vowel perception

Listeners perceive speech sounds relative to context. Contextual influences might differ over hemispheres if different types of auditory processing are lateralized. Hemispheric differences in contextual influences on vowel perception were investigated by presenting speech targets and both speech and non-speech contexts to listeners’ right or left ears (contexts and targets either to the same or to opposite ears). Listeners performed a discrimination task. Vowel perception was influenced by acoustic properties of the context signals. The strength of this influence depended on laterality of target presentation, and on the speech/non-speech status of the context signal. We conclude that contrastive contextual influences on vowel perception are stronger when targets are processed predominately by the right hemisphere. In the left hemisphere, contrastive effects are smaller and largely restricted to speech contexts.     

Hemispheric asymmetry for alphabetic identification: Scaling analyses

In a test of the analytic-holistic theory of hemispheric asymmetry, 20 subjects saw brief presentations of upper-case letters in either the left or right visual half-field. A right half-field advantage was found for both accuracy of identification and vocal latency of erroneous responses. Multidimensional scaling, hierarchical clustering, and correlation analyses of the error patterns indicated similarities of processing between the hemispheres. The results were discussed in terms of loss of information from storage prior to processing.     

Hemispheric asymmetry of slow brain potentials in relation to neuroticism

This report shows that neuroticism within low to medium range (EPI) is related to right hemisphere negative slow potential amplitudes at central leads (C₃ and C₄). This finding is interpreted as suggesting a relatively higher right hemisphere activation during a ‘classical’ fixed foreperiod reaction time task. It is discussed in relation to studies linking the right hemisphere to emotion and emotionality.     

Hemispheric asymmetry in the processing of absolute versus relative spatial frequency.

Observers indicated whether a stimulus presented to one visual field or the other consisted of two sine-wave gratings (the baseline stimulus) or those same two gratings with the addition of a 2 cycle per degree (cpd) component. When the absolute spatial frequencies of the baseline stimulus were low (0.5 and 1.0 cpd), there was a left visual field-right hemisphere (LVF-RH) advantage in reaction time (RT) to respond to the baseline stimulus which disappeared when the 2 cpd component was added (i.e., the stimulus consisted of 0.5, 1.0, and 2.0 cpd components). When the absolute spatial frequencies of the baseline stimulus were moderate to high (4.0 and 8.0 cpd), a right visual field-left hemisphere advantage in RT to respond to the baseline stimulus approached significance and shifted to a significant LVF-RH advantage when the 2 cpd component was added (i.e., the stimulus consisted of 2.0, 4.0, and 8.0 cpd components. That is, adding the same 2 cpd component caused opposite shifts in visual laterality depending on whether 2 cpd was a relatively high or relatively low frequency compared to the baseline.     

Processing steps in perception of speech sounds]

The aim of this study is to investigate whether speech sounds--as is stated by the widely accepted theory of categorical perception of speech--can be perceived only as instances of phonetic categories, or whether physical differences between speech sounds lead to perceptual differences regardless of their phonetic categorization. Subjects listened to pairs of synthetically generated speech sounds that correspond to realizations of the syllables "ba" and "pa" in natural German, and they were instructed to decide as fast as possible whether they perceived them as belonging to the same or to different phonetic categories. For 'same'-responses reaction times become longer when the physical distance between the speech sounds is increased; for 'different'-responses reaction times become shorter with growing physical distance between the stimuli. The results show that subjects can judge speech sounds on the basis of perceptual continua, which is inconsistent with the theory of categorical perception. A mathematical model is presented that attempts to explain the results by postulating two interacting stages of processing, a psychoacoustical and a phonetic one. The model is not entirely confirmed by the data, but it seems to deserve further consideration.     

Categorical perception of speech sounds in illiterate adults

Children affected by dyslexia exhibit a deficit in the categorical perception of speech sounds, characterized by both poorer discrimination of between-category differences and by better discrimination of within-category differences, compared to normal readers. These categorical perception anomalies might be at the origin of dyslexia, by hampering the set up of grapheme-phoneme correspondences, but they might also be the consequence of poor reading skills, as literacy probably contributes to stabilizing phonological categories. The aim of the present study was to investigate this issue by comparing categorical perception performances of illiterate and literate people. Identification and discrimination responses were collected for a /ba-da/ synthetic place-of-articulation continuum and between-group differences in both categorical perception and in the precision of the categorical boundary were examined. The results showed that illiterate vs. literate people did not differ in categorical perception, thereby suggesting that the categorical perception anomalies displayed by dyslexics are indeed a cause rather than a consequence of their reading problems. However, illiterate people displayed a less precise categorical boundary and a stronger lexical bias, both also associated with dyslexia, which might, therefore, be a specific consequence of written language deprivation or impairment.