Ambiguous emotion recognition in temporal lobe epilepsy: The role of expression intensity

The lateralization of emotion processing is currently debated and may be further explored by examining facial expression recognition (FER) impairments in temporal lobe epilepsy (TLE). Furthermore, there is also debate in the literature whether FER deficits in individuals with TLE are more pronounced in the right than in the left hemisphere. Individuals with TLE were tested with an FER task designed to be more sensitive than those classically used to shed light on this issue. A total of 25 right- and 32 left-TLE patients, candidates for surgery, along with controls, underwent an FER task composed of stimuli shown not only at full-blown intensities (100 %), but also morphed to lower-intensity display levels (35 %, 50 %, and 75 %). The results showed that, as compared to controls, right-TLE patients showed deficits in the recognition of all emotional categories. Furthermore, when considering valence, right-TLE patients were impaired only in negative emotion recognition, but no deficits for positive emotions were highlighted in left-TLE patients. Finally, only the right-TLE patients’ impairment was found to be related to the age of epilepsy onset. Our work demonstrates that the FER deficits in TLE span multiple emotional categories and show manifestations dependent on the laterality of the epileptic focus. Taken together, our findings provide the strongest evidence for the right-hemisphere model, but they also partially support the valence model. We suggest that current models are not exhaustive at explaining emotional-processing cerebral control, and further that multistep models should be developed.     

Controlled recall of verbal material in temporal lobe epilepsy

This study used a guided process‐dissociation procedure to examine the contribution of controlled and automatic uses of memory to a cued‐recall task in 24 patients with unilateral temporal lobe epilepsy (TLE: 12 left‐sided; 12 right‐sided), and 12 neurotypical controls. In an inclusion task, participants attempted to complete three‐letter word stems using previously studied words, in an exclusion task they aimed to avoid using studied words to complete stems. Patients with left TLE produced fewer target completions under inclusion conditions. Completion rates were not significantly different under exclusion conditions. Estimates derived from process dissociation calculations, confirmed that the cued‐recall deficit in left TLE patients arose entirely from impairment in controlled memory processes. There were no group differences in the estimates of automatic processes. Recognition judgements of stems corresponding to studied words did not differ between the groups. Overall the results support the view that controlled and automatic memory processes are mediated by separable neural systems. Hippocampal and related structures within the left MTL are more important than corresponding right hemisphere structures for the controlled retrieval of verbal material. In contrast, the findings from this study do not suggest that the left and right temporal lobes make a differential contribution to automatic memory processing. The theoretical and clinical relevance of these findings are discussed.     

Hemispheric specialization for processing of visually presented verbal and spatial stimuli

Two “same-different” reaction time experiments, analogous in task demands made on the S, were designed to test laterality differences in. perception. Ten normal right-handed Ss performed a verbal task in which they decided whether or not two three-letter words belonged to the same conceptual class. Ten different Ss performed a spatial task in which they decided whether two 16-cell matrices with 3 blackened cells were identical. Reaction times were found to be sensitive to laterality differences in perception. Verbal stimuli were processed faster when presented in the right visual field, and thus projected directly to the left cerebral hemisphere; spatial stimuli were processed faster when presented in the left visual field, and thus projected directly to the right cerebral hemisphere. These results were analyzed in terms of implications regarding hemispheric asymmetries for processing of verbal and spatial material and the nature of interhemispheric transfer of information.     

Dissociation of short- and long-term face memory: evidence from long-term recency effects in temporal lobe epilepsy

We tested whether memory deficits in temporal lobe epilepsy (TLE) are better described by a single- or dual-store memory model. To this aim, we analyzed the influence of TLE and proactive interference (PI) on immediate and 24-h long-term recency effects during face recognition in 16 healthy participants and 18 right and 21 left non-surgical TLE patients. PI in healthy participants or TLE erased the long-term recency effect, but left the immediate recency effect unaffected. Although the immediate recency effect was still visible in right TLE patients, the number of detected recency items during immediate recognition was decreased in right TLE compared to left TLE. Right TLE was also related to decreased detection of pre-recency items during delayed recognition compared to left TLE, and decreased detection of pre-recency items during immediate recognition under PI. The results show that the temporal lobes are necessary for the long-term recency effect, but not for the immediate recency effect, and thus speak for a dissociation of short- and long-term memory for faces. Right TLE is related to more severe long-term memory deficits than left TLE and is also related to additional short-term memory deficits for faces.     

Language after temporal or frontal lobe surgery in children with epilepsy

The purpose of this study was to compare language function in children undergoing temporal or frontal lobe surgery to control intractable epilepsy. Language measures (expressive vocabulary, receptive vocabulary, comprehension, reading, spelling, phonemic fluency, and category fluency) were administered to 9 children with frontal lobe epilepsy (mean age: 10.8 +/- 2.7 years) and 10 children with temporal lobe epilepsy (11.5 +/- 2.6 years). The results indicate that no differences exist, in language function, before and after surgery between children with frontal and temporal lobe epilepsy (all p > or = .05). Children with left hemisphere lesions had significantly lower scores than those with right on category fluency and comprehension, but laterality effects were not seen on the other measures. In both groups, language function was not significantly affected by surgery.     

Disruption of spelling-to-sound correspondence mapping during single-word reading in patients with temporal lobe epilepsy

Processing and/or hemispheric differences in the neural bases of word recognition were examined in patients with long-standing, medically-intractable epilepsy localized to the left (N=18) or right (N=7) temporal lobe. Participants were asked to read words that varied in the frequency of their spelling-to-sound correspondences. For the right temporal lobe group, reaction times (RTs) showed the same pattern across spelling-to-sound correspondence conditions as previously reported for normal participants. For the left temporal lobe group, however, the pattern of RTs suggested a greater relative influence of orthographic frequency than rime frequency, such that performance was worse on words whose orthographic body was less frequent in the language. We discuss these results in terms of differences in processing between the two cerebral hemispheres: the results for the right-temporal lobe patients are taken to support connectionist models of reading as described for the dominant (left) hemisphere, while results for the left-temporal lobe patients support a view of the right hemisphere as relatively less sensitive to phonology and relatively more sensitive to orthography.     

Dissociations among memory measures in memory-impaired subjects: Evidence for a processing account of memory

Deficits in conceptual transfer on both implicit and explicit memory tests were obtained for memory-impaired temporal lobe epileptic (TLE) subjects in three studies. In Experiment 1, in which a generate-read paradigm was employed, memory-impaired TLEs failed to show normal generation effects on conceptually driven tests of semantic cued recall and general knowledge questions, although their data-driven memory as measured by word-fragment completion and graphemic cued recall tasks was normal. In Experiment 2, memory-impaired patients having left temporal lobe seizure foci were tested on these four tasks and compared with nonimpaired TLEs having right temporal foci. The left TLEs showed deficits on conceptually driven tasks and normal memory for data-driven tests. These findings were extended in Experiment 3, in which left TLE patients failed to show any benefit from blocked study, as compared with random study, on category production and semantic cued-recall tests, although right TLEs and normal controls showed blocking effects on both tasks. These findings may be accommodated by a processing framework of memory in which memory-impaired patients are characterized as having deficits in conceptual, but not in data-driven, processing capabilities.     

Absence of exposure time influence on lateralized face recognition and object naming latency tasks

J. Sergent (1982, Perception & Psychophysics, 31, 451-461; 1983, Psychological Bulletin, 93, 481-512) postulates that the left cerebral hemisphere preferentially extracts higher spatial frequency information, while the right hemisphere preferentially extracts lower frequency spatial information, from the visual scene. According to this view, shorter exposure times favor better right than left hemisphere performance, while longer exposure times favor better left than right hemisphere performance on tachistoscopic laterality tasks. We studied the effects of a threefold variation (40 msec versus 120 msec) in exposure duration, with constant 3-mL luminance, on face recognition and on object naming latency task performances. These are the same stimulus parameters employed by J. Sergent (1983, Psychological Bulletin, 93, 481-512) to demonstrate exposure duration effects in a task requiring the judgment of the sex of models from face photographs. We found the expected LVF superiority on the face recognition task and RVF superiority on the object naming task. There was, however, no influence of exposure duration on the performances. It is concluded that these tasks, which tap established lateralized processing asymmetries, are quite robust in their resistance to exposure time influence.     

Attention and hemispheric differences in reaction time during simultaneous audio-visual tasks

The effect of different types of competing auditory tasks on laterality differences in visual perception was investigated. Right-handed subjects were presented with digits which occurred randomly in the left or right visual fields. They responded vocally to previously specified digits in a go, no-go reaction time situation. In the absence of any competing auditory task, digits presented in the right visual field were processed more quickly. This visual field difference in reaction time was in the same direction while subjects performed a secondary musical task. However, when a secondary verbal task had to be performed, digits in the left visual field received faster responses. The results support the view that the right hemisphere is capable of some language functions, and that hemispheric differences in performance have at their basis a quantitative asymmetry, which can be reversed even in normal subjects by overloading their limited capacity.     

Neurodevelopmental differences in emotional prosody in normal children and children with left and right temporal lobe epilepsy

Emotional prosody, which has been defined as the emotional aspects of speech which communicate pleasure, fear, sorrow, anger, etc., has been demonstrated to be primarily a function of the nondominant hemisphere (typically, the right hemisphere) in adult populations. However, few researchers have addressed the developmental or lateralized nature of emotional prosody in children. In this study, an instrument was developed to measure the receptive aspects of emotional prosody in pediatric populations and administered to normal children ages 6 to 11 years old. An analysis of variance revealed significant age-related differences. Additionally, the instrument was administered to 12 children with right temporal lobe epilepsy and 11 children with left temporal lobe epilepsy. Analysis of variance indicated that there was no significant difference in scores between the left temporal and right temporal lobe groups. However, right temporal epileptic patients scored significantly lower than normal children on all sections of the instrument, suggesting that in children like adults, the right temporal lobe may be dominant with respect to the receptive aspects of emotional prosody.     

Bimanual tapping of a syncopated rhythm reveals hemispheric preferences for relative movement frequencies

In bimanual multifrequency tapping, right-handers commonly use the right hand to tap the relatively higher rate and the left hand to tap the relatively lower rate. This could be due to hemispheric specializations for the processing of relative frequencies. An extension of the double-filtering-by-frequency theory to motor control proposes a left hemispheric specialization for the control of relatively high and a right hemispheric specialization for the control of relatively low tapping rates. We investigated timing variability and rhythmic accentuation in right handers tapping mono- and multifrequent bimanual rhythms to test the predictions of the double-filtering-by-frequency theory. Yet, hemispheric specializations for the processing of relative tapping rates could be masked by a left hemispheric dominance for the control of known sequences. Tapping was thus either performed in an overlearned quadruple meter (tap of the slow rhythm on the first auditory beat) or in a syncopated quadruple meter (tap of the slow rhythm on the fourth auditory beat). Independent of syncopation, the right hand outperformed the left hand in timing accuracy for fast tapping. A left hand timing benefit for slow tapping rates as predicted by the double-filtering-by-frequency theory was only found in the syncopated tapping group. This suggests a right hemisphere preference for the control of slow tapping rates when rhythms are not overlearned. Error rates indicate that overlearned rhythms represent hierarchically structured meters that are controlled by a single timer that could potentially reside in the left hemisphere.     

Role of the left hemisphere in sign language comprehension

We investigated the relative role of the left versus right hemisphere in the comprehension of American Sign Language (ASL). Nineteen lifelong signers with unilateral brain lesions [11 left hemisphere damaged (LHD) and 8 right hemisphere damaged (RHD)] performed three tasks, an isolated single-sign comprehension task, a sentence-level comprehension task involving simple one-step commands, and a sentence-level comprehension task involving more complex multiclause/multistep commands. Eighteen of the participants were deaf, one RHD subject was hearing and bilingual (ASL and English). Performance was examined in relation to two factors: whether the lesion was in the right or left hemisphere and whether the temporal lobe was involved. The LHD group performed significantly worse than the RHD group on all three tasks, confirming left hemisphere dominance for sign language comprehension. The group with left temporal lobe involvement was significantly impaired on all tasks, whereas each of the other three groups performed at better than 95% correct on the single sign and simple sentence comprehension tasks, with performance falling off only on the complex sentence comprehension items. A comparison with previously published data suggests that the degree of difficulty exhibited by the deaf RHD group on the complex sentences is comparable to that observed in hearing RHD subjects. Based on these findings we hypothesize (i) that deaf and hearing individuals have a similar degree of lateralization of language comprehension processes and (ii) that language comprehension depends primarily on the integrity of the left temporal lobe.     

The role of the cerebral hemispheres in music.

This review examines the cerebral control of musical behaviors. In clinical populations, impairment of related musical and linguistic functions, such as reading, writing, articulation, time sense, and prosody, implies the likely role of the language hemisphere in music. Similarly, for both clinical and normal populations, an investigation of mental abilities common to music and language points to left hemisphere control for certain aspects of temporal order, duration, simultaneity, rhythm, effector motor control, and categorical perception. While clinical studies have revealed deficits in various kinds of music capabilities with both left and right cerebral lesions, normal subjects similarly demonstrate varying degrees of asymmetry for components of music emphasizing pitch, harmony, timbre, intensity, and rhythm. Since differential laterality effects are apparent as a function of subjects' training or adopted strategies, the way musical information is processed may be an important determinant of hemispheric mediation. One hemisphere should not be regarded as “dominant” for music, but rather each interacts with the other, operating according to its own specialization.     

Rhyming and the right hemisphere

Subjects determined whether two successively presented and orthographically different words rhymed with each other. The first word was presented at fixation and the second was presented either to the left or to the right of fixation, either alone (unilateral presentation) or accompanied by a distractor word in the other visual hemifield (bilateral presentation). Subjects were more accurate when the words did not rhyme, when presentation was unilateral, and when the target was flashed to the right visual hemifield. It was predicted that bilateral presentation would produce interference when information from both visual fields was processed by one hemisphere (callosal relay), but not when each of the two hemispheres performed a task independently (direct access). That is, callosal relay tasks should show greater laterality effects with bilateral presentations, whereas direct access tasks should show similar laterality effects with both bilateral and unilateral presentations. Greater laterality effects were observed for bilaterally presented rhyming words, but nonrhyming words showed similar laterality effects for both bilateral and unilateral presentations. These results suggest that judgment of nonrhyming words can be performed by either hemisphere, but that judgment of rhyming words requires callosal relay to the left hemisphere. The absence of a visual field difference with nonrhyming word pairs suggests further that judgment of nonrhyming word pairs may be accomplished by the right hemisphere when presentation is to the left visual field.     

Can small lesions induce language reorganization as large lesions do?

Shift of the cortical mechanisms of language from the usually dominant left to the non-dominant right hemisphere has been demonstrated in the presence of large brain lesions. Here, we report a similar phenomenon in a patient with a cavernoma over the anterolateral superior temporal gyrus associated with epilepsy. Language mapping was performed by two complementary procedures, magnetoencephalography, and electrocorticography. The maps, indicated right temporal lobe dominance for receptive language and left frontal lobe dominance for expressive language. These results indicate that a small lesion, associated with epilepsy, may produce selective shifting of receptive language mechanisms as large lesions have been known to produce.     

Dichotic listening with forced attention in patients with temporal lobe epilepsy: significance of left hemisphere cognitive dysfunction

Fifty right-handed patients with focal temporal lobe epilepsy were administered a dichotic listening test with consonant-vowel syllables under non-forced, forced right and forced left attention conditions, and a neuropsychological test battery. Dichotic listening performance was compared in subgroups with and without left hemisphere cognitive dysfunction, measured by the test battery, and in subgroups with left and right temporal epileptic focus. Left hemisphere cognitive dysfunction led to more correct responses to left ear stimuli in all three attention conditions, and fewer correct responses to right ear stimuli in the non-forced attention condition. This was probably caused by basic left hemisphere perceptual dysfunction. Dichotic listening was less affected by a left-sided epileptic focus than by left hemisphere cognitive dysfunction. General cognitive functioning influenced dichotic listening performance stronger in forced than in non-forced attention conditions. Larger cerebral networks were probably involved in the forced attention conditions due to the emphasis on conscious effort.     

Rhythmic information in working memory: effects of concurrent articulation on reproduction of rhythms

The study addressed a previously neglected issue in the concept of working memory, namely whether or not rhythmical information is coded and maintained in a phonological loop. Thirty subjects engaged in a task which required them to reproduce the temporal sequence of rhythm. The results showed that the reproduction of rhythm was dramatically reduced by a concurrent articulation, and that the deterioration of rhythm reproduction was larger than that obtained with a concurrent spatial task which would not diminish the activity of the phonological loop directly. An articulatory component of the working memory apparently plays an important role in memorizing rhythms. Furthermore, the sparse-dense rhythm (a pattern which started with sparse temporal structure and ended with a dense one) allowed better memorization than a dense-sparse pattern. The sources of the sparse-dense superiority effect are discussed in terms of the working memory for rhythmic information.     

Rhythm and Melody in Children and Adolescents after Left or Right Temporal Lobectomy

Rhythm (a pattern of onset times and duration of sounds) and melody (a pattern of sound pitches) were studied in 22 children and adolescents several years after temporal lobectomy for intractable epilepsy. Left and right lobectomy groups discriminated rhythms equally well, but the right lobectomy group was poorer at discriminating melodies. Children and adolescents with right lobectomy, but not those with left temporal lobectomy, had higher melody scores with increasing age. Rhythm but not melody was related to memory for the right lobectomy group. In neither group was melody related to age at onset of non-febrile seizures, time from surgery to music tests, or the linear amount of temporal lobe resection. Pitch and melodic contour show different patterns of lateralization after temporal lobectomy in childhood or adolescence.     

Do temporal processes underlie left hemisphere dominance in speech perception?

It is not unusual to find it stated as a fact that the left hemisphere is specialized for the processing of rapid, or temporal aspects of sound, and that the dominance of the left hemisphere in the perception of speech can be a consequence of this specialization. In this review we explore the history of this claim and assess the weight of this assumption. We will demonstrate that instead of a supposed sensitivity of the left temporal lobe for the acoustic properties of speech, it is the right temporal lobe which shows a marked preference for certain properties of sounds, for example longer durations, or variations in pitch. We finish by outlining some alternative factors that contribute to the left lateralization of speech perception.