Associations and dissociations of transitive and intransitive gestures in left and right hemisphere stroke patients

The study investigated performance on pantomime and imitation of transitive and intransitive gestures in 80 stroke patients, 42 with left (LHD) and 38 with right (RHD) hemisphere damage. Patients were also categorized in two groups based on the time that has elapsed between their stroke and the apraxia assessment: acute–subacute (n = 42) and chronic (n = 38). In addition, patterns of performance in apraxia were examined. We expected that acute–subacute patients would be more impaired than chronic patients and that LHD patients would be more impaired than RHD patients, relative to controls. The hemisphere prediction was confirmed, replicating previous findings. The frequency of apraxia was also higher in all LHD time post-stroke groups. The most common impairment after LHD was impairment in both pantomime and imitation in both transitive and intransitive gestures. Selective deficits in imitation were more frequent after RHD for transitive gestures but for intransitive gestures they were more frequent after LHD. Patients were more impaired on imitation than pantomime, relative to controls. In addition, after looking at both gesture types concurrently, we have described cases of patients who suffered deficits in pantomime of intransitive gestures with preserved performance on transitive gestures. Such cases show that the right hemisphere may be in some cases critical for the successful pantomime of intransitive gestures and the neural networks subserving them may be distinct. Chronic patients were also less impaired than acute–subacute patients, even though the difference did not reach significance. A longitudinal study is needed to examine the recovery patterns in both LHD and RHD patients.     

Numbers and space: a computational model of the SNARC effect

The SNARC (spatial numerical associations of response codes) effect reflects the tendency to respond faster with the left hand to relatively small numbers and with the right hand to relatively large numbers (S. Dehaene, S. Bossini, & P. Giraux, 1993). Using computational modeling, the present article aims to provide a framework for conceptualizing the SNARC effect. In line with models of spatial stimulus-response congruency, the authors modeled the SNARC effect as the result of parallel activation of preexisting links between magnitude and spatial representation and short-term links created on the basis of task instructions. This basic dual-route model simulated all characteristics associated with the SNARC effect. In addition, 2 experiments tested and confirmed new predictions derived from the model.     

Double dissociations and neurophysiological expectations

Double dissociations are among the most highly regarded and influential evidence for particular modular divisions of cognitive performance. We present here a method for obtaining double dissociations across any task, even within an avowedly indivisible and unmodular system. We argue that the existence of double dissociations is not necessarily evidential and suggest what sort of additional evidence would be necessary to support the desired conclusions. We suggest that the idea of expected behavior after injury is important and should receive more attention.     

The disruption of sentence production: some dissociations

A patient (M.L.) with selective disruption of sentence production is described. M.L.'s sentence production performance is characterized by the omission (and occasional substitution) of free-standing and bound grammatical morphemes. In contrast to her impaired sentence production performance, M.L. has no difficulties in sentence comprehension or production of single words including functors. Her performance is interpreted as reflecting a functional lesion to the positional level of sentence production.     

Forward inference using functional neuroimaging: dissociations versus associations

Many people are excited by functional neuroimaging as a new tool for cognitive science; many others are sceptical. In this opinion article, I describe a 'forward inference' that one can make from patterns of brain activity to distinguish between cognitive theories. I give an example of forward inferences in research on recognition memory, and outline some statistical criteria for a 'qualitative difference' in brain activity. Forward inferences resemble the dissociation logic long-used in behavioural studies of healthy and brain-damaged people, although I argue that dissociations in neuroimaging data can go beyond behavioural dissociations. Nonetheless, forward inferences are only as good as the cognitive theories to which they pertain, and are most valuable in conjunction with other types of inference.     

Item-specific control of automatic processes: Stroop process dissociations

The influence of word reading on Stroop color naming decreases as a function of the proportion of test items that are incongruent. This proportion-congruent effect is usually ascribed to strategies (e.g., maintaining task set) that operate at a general level to moderate the extent to which participants are influenced by word reading. However, in three experiments, effects at the level of specific items were found. Interference and facilitation were smaller for color names usually presented in an incongruent color than for color names usually presented in their congruent colors. This item-specific proportioncongruent manipulation affected the process dissociation (PD) estimate of the influence of word-reading processes but not that of color-naming processes. The results (1) indicate that item-specific, as opposed to general, mechanisms can reduce the influence of word-reading processes on Stroop performance and (2) demonstrate the PD procedure’s utility in studying Stroop phenomena.     

Neuropsychological dissociations between priming and recognition: a single-system connectionist account

A key claim of current theoretical analyses of the memory impairments associated with amnesia is that certain distinct forms of learning and memory are spared. A compelling example is that amnesic patients and controls are indistinguishable in repetition priming but amnesic patients are impaired at recognizing the study items. The authors show that this pattern of results is predicted by a single-system connectionist model of learning in which amnesia is simulated by a reduced learning rate. They also demonstrate that the model can reproduce the converse pattern in which priming but not recognition is impaired if the input is assumed to be additionally degraded in a priming test. The authors conclude that dissociations between priming and recognition do not require functionally or neurally distinct memory systems.     

On testing for stochastic dissociations

Methods for examining stochastic relationships have been proposed as powerful ways to dissociate different underlying psychological processes, but a number of problems have undermined conclusions based upon these methods. These testing methods and criticisms are reviewed, and the statistical methods for the testing of stochastic dependence are examined using computer simulation. With each of the methods examined, there were difficulties dealing with certain situations that are likely to occur in experiments examining dependence between successive tests. Examination also showed that the sample sizes of some previous studies were insufficient for findings of moderate amounts of dependence, calling some conclusions of stochastic independence into question. The results of the studies presented here suggest that testing for statistical dependence is a statistically perilous technique, but they also suggest several ways in which dedicated users of this form of testing can strengthen its application.     

Childhood stuttering and dissociations across linguistic domains

The purpose of this investigation was to evaluate the possible presence of dissociations in the speech and language skills of young children who do (CWS) and do not stutter (CWNS) using a correlation-based statistical procedure [Bates, E., Appelbaum, M., Salcedo, J., Saygin, A. P., & Pizzamiglio, L. (2003). Quantifying dissociations in neuropsychological research. Journal of Clinical and Experimental Neuropsychology, 25, 1128-1153]. Participants were 45 preschool CWS and 45 CWNS between the ages of 3;0 and 5;11 (years;months), with the two groups matched by age, gender, race, and parental socioeconomic status. Children participated in a parent-child interaction for the purpose of disfluency analysis and responded to four standardized speech-language tests for subsequent analyses as main dependent variables. Findings indicated that CWS were over three times more likely than CWNS to exhibit dissociations across speech-language domains, with 44 cases of dissociation for CWS and 14 for CWNS across 10 possible comparisons. Results suggest that there may be a subgroup of CWS who exhibit dissociations across speech-language domains, which may result in a greater susceptibility to breakdowns in speech fluency. EDUCATIONAL OBJECTIVES: The reader will be able to: (1) summarize findings from previous studies examining differences in speech and language performance between children who do and do not stutter; (2) describe what is meant by "dissociations" in the speech and language skills of young children who do and do not stutter; and (3) discuss three hypotheses that could account for the present findings that suggest CWS, more often than CWNS, exhibit dissociations in their speech-language system.     

All together now: when dissociations between knowledge and action disappear

Why do people sometimes seem to know things but fail to act appropriately on the basis of this knowledge? Such dissociations between knowledge and action often occur in infants and children, and in adults following brain damage. These dissociations have supported inferences about the organization of cognitive processes (e.g., separable knowledge and action systems) and their development (e.g., knowledge systems develop before action systems). The current study tested the basis for knowledge-action dissociations in a card-sorting task in which children typically correctly answer questions about sorting rules while sorting cards incorrectly. When questions and sorting measures were more closely equated for the amount of conflict that needed to be resolved for a correct response, children showed no systematic dissociation between knowledge and action. The results challenge standard interpretations of knowledge-action dissociations and support an alternative account based on graded knowledge representations.     

Functional localization and double dissociations: the relationship between internal structure and behavior

Lesioning studies are often used in cognitive neuroscience to make inferences about the architecture of cognition. Recently, computational models have been used to address some of the underlying assumptions-such as modularity and locality-often implicitly used when interpreting lesion data. In this article, we explore the "functional localization" assumption and its role in interpreting lesioning data, especially from double dissociations. The functional localization assumption states that units or subunits within an information processing system become functionally specialized for dealing with specific aspects of the input environment. Networks were trained on one of two problems-an abstract "rules and sub-rules" problem, and a more concrete "logic classification" problem-and then systematically lesioned. Networks were analyzed in terms of their overt behavior, and more importantly, in terms of their internal structure. Performance deficits in both form and magnitude could be directly related to the ablated internal structure of the networks. That is, if an ablated area had little or no functional localization, then little or no behavioral dissociations were observed. If, however, the ablated area had very specific internal structure, then very specific behavioral dissociations were observed. It is important to note, however, that there was not a one-to-one correspondence between internal structure and behavioral dissociations, implying that cognitive neuroscientists must be careful when using lesioning data to theorize about the functional architecture of cognition.     

Feedback interference and dissociations of classification: Evidence against the multiple-learning-systems hypothesis

Researchers have argued that different categorization problems are learned by separate and distinct cognitive systems. They propose that an explicit system is responsible for learning rule-based categories and that a separate implicit system learns information-integration categories. One source of supporting evidence involves experiments in which observers perform a concurrent memory-scanning task that interferes with the processing of feedback. Researchers have reported a dissociation in which this manipulation impairs learning of a rule-based category but not an information-integration category. In the present research, we test the hypothesis that the dissociation was the result of lowered perceptual discriminability in the rule-based structure in comparison with the information-integration one. We demonstrate an example of an alternate rule-based category with easy-to-discriminate stimuli in which performance is unaffected by the interfering memory-scanning task. Furthermore, we demonstrate that learning of an information-integration category with low perceptual discriminability is impaired by the memory-scanning task. These demonstrations of the reverse dissociation challenge the interpretation that rule-based and information-integration category structures are learned by separate cognitive systems.     

Functional dissociations in temporal preparation: Evidence from dual-task performance

Implicit preparation over time is a complex cognitive capacity important to optimize behavioral responses to a target occurring after a temporal interval, the so-called foreperiod (FP). If the FP occurs randomly and with the same a priori probability, shorter response times are usually observed with longer FPs than with shorter ones (FP effect). Moreover, responses are slower when the preceding FP was longer than the current one (sequential effects). It is still a matter of debate how different processes influence these temporal preparation phenomena. The present study used a dual-task procedure to understand how different processes, along the automatic-controlled continuum, may contribute to these temporal preparation phenomena. Dual-task demands were manipulated in two experiments using a subtraction task during the FP. This secondary task was administered in blocks (Experiment 1) or was embedded together with a baseline single-task in the same experimental session (Experiment 2). The results consistently showed that the size of the FP effect, but not that of sequential effects, is sensitive to dual-task manipulations. This functional dissociation unveils the multi-faceted nature of implicit temporal preparation: while the FP effect is due to a controlled, resource-consuming preparatory mechanism, a more automatic mechanism underlies sequential effects.     

Experimental dissociations between memory measures: Influence of retrieval strategies

The objective of this study was to explore the participants’ processing strategies on the mere exposure effect, object decision priming and explicit recognition. In Experiments 1, we observed that recognition and the mere exposure effect for unfamiliar three-dimensional objects were not dissociated by plane rotations in the same way as recognition and object decision priming. However, we showed that, under identical conditions, prompting analytic (part-based) processing at testing produced a large plane rotation effect on recognition and the mere exposure effect similar to that observed for object decision priming (Experiment 2). Furthermore, inducing a non-analytic (whole-based) processing strategy at testing produced a reduced plane rotation effect on recognition and object decision (Experiments 3 and 4), similar to that observed for the mere exposure effect. These findings suggest that participants’ processing strategies influence performance on the three tasks.     

Double dissociations in visual and spatial short-term memory

A visual short-term memory task was more strongly disrupted by visual than spatial interference, and a spatial memory task was simultaneously more strongly disrupted by spatial than visual interference. This double dissociation supports a fractionation of visuospatial short-term memory into separate visual and spatial components. In 6 experiments, this interpretation could be defended against alternative explanations in terms of trade-offs in resource allocation between memory tasks and interference tasks, in terms of an involvement of short-term consolidation and long-term memory, in terms of differential phonological-loop and central-executive involvement, and in terms of similarity-based interference.     

Tense and Agreement dissociations in German agrammatic speakers: underspecification vs. hierarchy

The aim of the present paper was to investigate whether German agrammatic production data are compatible with the Tree-Pruning-Hypothesis (TPH; Friedmann & Grodzinsky, 1997). The theory predicts unidirectional patterns of dissociation in agrammatic production data with respect to Tense and Agreement. However, there was evidence of a double dissociation between Tense and Agreement in our data. The presence of a bidirectional dissociation is incompatible with any theory which assumes a hierarchical order between these categories such as the TPH or other versions thereof (such as Lee's, 2003 top--down hypothesis). It will be argued that the data can better be accounted for by relying on newer linguistic theories such as the Minimalist Program (MP,), which does not assume a hierarchical order between independent syntactic Tense and Agreement nodes but treats them as different features (semantically interpretable vs. uninterpretable) under a single node.     

More dissociations and interactions within central executive functioning: a comprehensive latent-variable analysis

The present study examined the separability of six executive functions (verbal storage-and-processing coordination, visuospatial storage-and-processing coordination, dual-task coordination, strategic retrieval, selective attention, and shifting) and their relationships, by means of confirmatory factor analysis. A set of tasks thought to primarily assess each target function was administered to 180 participants. The results demonstrated that five of the six functions initially considered were distinguishable albeit related constructs, with one of these functions combining inhibitory and strategic retrieval processes. The analyses failed to reveal a single dual-task coordination ability underlying performance on the dual-tasks. These findings provide further support for the fractionation of the central executive into several functions and also stress the need to approach executive functioning in terms of both dissociations within general functions and specific interactions between some of these functions.     

Doubts about double dissociations between short- and long-term memory

Historically, psychologists and neuroscientists have distinguished between processes supporting memory for events across retention delays of several seconds (short-term memory, STM), and those supporting memory for events across longer retention delays of minutes or more (long-term memory, LTM). Dissociations reported in some neuropsychological studies have contributed to a popular view that there must be neurally distinct memory stores that differentially support STM and LTM. In this article, we review evidence from recent studies regarding dissociations between STM and LTM. We suggest that the evidence reveals problems with claims of selective STM or LTM impairments, which in turn questions whether theories of memory need to propose neurally distinct stores for short- and long-term retention. We consider alternative ways to explain the neural mechanisms of memory across different retention intervals.     

Interpreting dissociations between regular and irregular past-tense morphology: Evidence from event-related potentials

Neuropsychological dissociations between regular and irregular English past-tense morphology have been reported using a lexical decision task in which past-tense primes immediately precede present-tense targets. We present N400 event-related potential data from healthy participants using the same design. Both regular and irregular past-tense forms primed corresponding present-tense forms, but with a longer duration for irregular verbs. Phonological control conditions suggested that differences in formal overlap between prime and target contribute to, but do not account for, this difference, suggesting a link between irregular morphology and semantics. Further analysis dividing the irregular verbs into two categories (weak irregular and strong) revealed that priming for strong verbs was reliably stronger than that for weak irregular and regular verbs, which were statistically indistinguishable from one another. We argue that, although we observe a regular-irregular dissociation, the nature of this dissociation is more consistent with single- than with dual-system models of inflectional morphology.     

Knowledge of object manipulation and object function: dissociations in apraxic and nonapraxic subjects

An influential account of selective semantic deficits posits that visual features are heavily weighted in the representations of animals, whereas information about function is central in the representations of tools (e.g., Warrington & Shallice, 1984 ). An alternative account proposes that information about all types of objects-animate and inanimate alike-is represented in a distributed semantic architecture by verbal-propositional, tactile, visual, and proprioceptive-motor nodes, reflecting the degree to which these systems were activated when the knowledge was acquired (e.g., Allport, 1985 ). We studied a group of left hemisphere chronic stroke patients, some of whom were apraxic, with measures of declarative tool and animal knowledge, body part knowledge, and function and manipulation knowledge of artifacts. Apraxic (n=7) and nonapraxic (n=6) subjects demonstrated a double dissociation of performance on tests of tool and animal knowledge, suggesting that the apraxic group was not simply more severely impaired overall. Apraxics were relatively impaired in manipulation knowledge, whereas nonapraxics tended to be relatively impaired in function knowledge. Apraxics were also more impaired with body parts than nonapraxics. The association of gestural praxis, tool knowledge, body part knowledge, and manipulation knowledge suggests a coherent basis for the organization of semantic artifact knowledge in frontoparietal cortical regions specialized for sensorimotor functions, and thus provides support for the distributed architecture account of the semantic system.