Cerebral lateralization in bilinguals: Methodological issues

The literature on lateralization for language in bilinguals manifests two apparent contradictions. Some papers demonstrate differences in lateralization between bilinguals and monolinguals; others demonstrate none. In studies with exclusively bilingual subjects, some papers demonstrate differences between the lateralization for the two languages, while others demonstrate none. This paper discusses the range of methodological parameters which must be borne in mind when conducting or evaluating studies of lateralization for language in bilinguals. These include issues of subject selection, language and stimulus selection, testing procedures, data analysis, and interpretation of results.     

Reversal operations after brain damage

The ability to perform reversals—that is, the appreciation of the relationship between original and transformed states of knowledge—is critical to human thought processes. In order to assess whether a number of “special-purpose processors” are responsible for reversal operations, depending on the particular context in which the reversal is couched, or whether a single “core processing mechanism” subserves a critical aspect of reversal operations regardless of the specific context, patients with localized brain damage were asked to solve eight reversal problems. Visual and auditory reversals mediated by linguistic and non-linguistic symbol systems were presented. The findings demonstrate that patients with insult to the anterior portion of the right hemisphere encounter more difficulty performing reversals than patients with right posterior insult, Broca's aphasics, and fluent aphasics. This is regardless of the symbol system mediating the reversal, regardless of the modality of presentation, and regardless of the amount of available processing time. Subjects with insult to the posterior region of the left hemisphere or the right hemisphere also exhibit some difficulty solving reversal problems, although their difficulties appear modality specific. These data lend support to the claim that a core processing mechanism may play a critical role in the performance of reversal operations.     

Filling gaps: Decision principles and structure in sentence comprehension

The correct grammatical characterization of sentences containing filler-gap dependencies is a topic of considerable theoretical interest in linguistics. In some grammatical frameworks, these dependencies are representef in terms of conditions on the permissible indexing of structures (or alternative structure evaluation conditions) which a representation must adhere to in order to be well-formed. In other frameworks, constraints on permissible filler-gap dependencies are simply inherent in the set of phrase structure rules contained in the grammar of a language.The processing of sentences with multiple (potential) filler-gap dependencies was investigated in two experiments. The first experiment provided evidence for three claims. First, the human sentence processor abides by a strategy of assigning the most recent potential filler to a gap. Hence, ‘recent filler’ sentences where this assignment proves to be correct takes less time to comprehend than ‘distant filler’ sentences where this decision turns out to be incorrect. Second, the recent filler strategy is itself just a special case of a more general strategy of assigning the most salient potential filler to a gap. Third, unambiguous sentences in which a filler-gap assignment is disambiguated by ‘control’ information specified by individual verbs gives rise to the same recent filler errors as ambiguous sentences. This suggests that tentative filler-gap assignments are made by the processor before all of the relevant constraints on permissible filler-gap dependencies are consulted by the processor.The second experiment tested an alternative hypothesis that the more complex ‘distant filler’ sentences took longer to comprehend in the first experiment only because these sentences often contained verbs which license two adjacent gaps. The experiment showed that there was a significant recent filler effect in sentences that did not contain adjacent gaps and that this effect did not interact with verb class.The finding that the processor delays use of verb-control information is extremely surprising. It may be explained by the fact that this information is only relevant to one type of gap (‘equi-gaps’) and what type of gap the processor is dealing with often can not be determined unambiguously at the time when it initially encounters a gap in its left-to-right processing of a sentence.If our interpretation of these findings is correct, they argue for a considerable amount of structure in the sentence comprehension system. Further, they favor a view of sentence processing in which processing operations involving constraints on the permissible indexing (or evaluation) of structures lag behind the processor's structure building operations. Hence, the results favor those grammatical theories which preserve this distinction over grammatical theories which provide a uniform characterization of all syntactic well-formedness conditions.     

Surprise but not coherence: Sensitivity to verbal humor in right-hemisphere patients

Verbal humor deficits were investigated in right-hemisphere-damaged patients. It was hypothesized that the appreciation of jokes presupposes two elements: sensitivity to the surprise element entailed in the punch line of a joke and apprehension of the coherence which results when the punch line has been integrated with the body of the joke. The possible dissociation between these elements was tested by asking subjects to select from four alternatives the appropriate ending to a joke. Right-hemisphere patients exhibited a selective attraction to endings which contained an element of surprise but which were not otherwise coherent with the body of the joke. This finding suggests that right-hemisphere patients have difficulty in integrating content across parts of a narrative and confirms the psychological reality of the proposed distinction between the surprise and coherence elements of humor processing.     

Keeping track of locations during movement in 8- to 10-month-old infants

Infants of $\text{8}\text{1}\text{2}$ and $\text{9}\text{1}\text{2}$ mo of age were tested for the ability to “keep track,” i.e., to determine the location of an object hidden in one of two covered containers before their left-right positions were reversed. Infants in both age groups for whom the covers were the same color and younger infants for whom the covers were different colors were generally unable to keep track. Only the older infants provided with different colored covers were able to do so. An analysis which separated keeping track from the sensorimotor stage 4 error indicated that (a) there was no contingency between the two and (b) there were developmental differences in the nature of the error.     

Profiles of symbol-reading skills in organic patients

One (unitary) school of thought views all symbolic competences as closely related, while a rival (pluralistic) approach underscores the relative differences among modes of symbolic processing. To secure information on the plausibility of these competing hypotheses, matched groups of left- and right-hemisphere patients were given a visual symbol-recognition test. Subjects were required to choose the correctly depicted symbol among a set of four. The results challenge a strong version of the “unitary” hypothesis. What emerges instead is a view of symbol systems as a continuum: relatively linguistic symbol systems prove challenging for left-hemisphere patients, relatively nonlinguistic systems pose comparable difficulties for right-hemisphere patients. Contrary to hypothesis, the processing of numerical symbols poses special difficulty for right-hemisphere patients. Performance on trademarks—items which can be processed by linguistic or nonlinguistic strategies—suggests that organic patients with contrasting pathologies may adopt different processing strategies when confronting identical physical stimuli.     

Semantic field,naming, and auditory comprehension in aphasia

The status of semantic fields for 16 target nouns was compared in high and low comprehension aphasics, brain damaged, and normal controls, by measuring latency and miss rate for recognition of six classes of associates, which were presented orally on tape. The ability to name each target was also examined as a function of the integrity of the subject's semantic field for that word. Low comprehension aphasics showed both quantitative and qualitative changes in semantic fields, while milder aphasics showed only mild quantitative impairment, as compared to controls. Both latency and miss rate measures indicated that failure to name a word is associated with reduced semantic field for that word. This result is interpreted as supporting the view that nameing is, in part, determined by the convergence of associations.     

Rehearsal strategies of Alcoholic Korsakoff patients

An overt rehearsal procedure was used to monitor the rehearsal strategies that Alcoholic Korsakoff, Chronic Alcoholic, and Normal Control patients used when learning a 20-item list. It was found that Korsakoff patients spontaneously rehearse only one word at a time, that word being the one currently presented, regardless of the organizational salience of the list of words. Alcholics and Control patients, on the other hand, tended to rehearse several words in addition to the one being currently presented, and they demonstrated increasing ability to rehearse semantically related words together as the organizational salience of the list increased. This ability to rehearse in an enriched manner placed the two control groups at a distinct advantage over the Korsakoff patients at the time of recalling the list.     

Arousal and memory: phasic measures of arousal in a free recall task.

EEG alpha activity and skin potential were monitored during word presentation in a single trial free recall task. Phasic changes in EEG alpha and skin potential, co-occurring with word onset, were positively related to recall at an immediate retention interval (2 min) but not after a delay (45 min). The results were interpreted as supporting the extension of Routtenberg's (1968) two-arousal system hypothesis to human memory. Arousal was viewed as affecting memory during the attribute encoding stage of memory storage.     

A developmental study of the effects of irrelevant information on speeded classification

The study examined how well subjects were able to ignore the presence of irrelevant stimulus information as a function of age. Children aged 6, 9, and 12, as well as adult subjects sorted cards with one binary dimension relevant, and zero, one, or two dimensions irrelevant. Speed of classification was measured. Significant effects of age, sex, number of irrelevant dimensions, and relevant dimension on speed of classification were obtained, as well as a number of interactions of these variables. The most important finding was that the presence of irrelevant information interfered with the performance of the task by child subjects and that the magnitude of the interference declined with age. The results were interpreted as implying that developmental trends in attention may be most clearly demonstrated in tasks which require speeded processing of stimuli. The ease of administration of the speeded classification task, coupled with the clear developmental trends obtained, recommend this paradigm as a useful one with which to study the development of selective attention.