Old age is associated with a pattern of relatively intact and relatively impaired task-set switching abilities.

In three experiments, we examined the effects of old age on the reaction time (RT) decrement associated with task alternation. Old age was associated with increased mixing-cost, which is the RT difference between two conditions: mixed-task, where trials involving two tasks were intermixed, and single-task, where all the trials involved the same task. Old age was also associated with an increased switching-cost, which is the RT difference between trials in which the task was just changed and trials in which it was repeated. There was also indication of a slowed passive dissipation of task set adopted in the preceding trial. In contrast to these impairments, old age was also associated with an almost intact ability to prepare for an upcoming task switch. This ability was indicated by a normal reduction in switching-cost due to an increase in the time allowed to prepare for the switch. We discuss the implications of the results in relation to theories of task-switching and to the underlying brain mechanisms, especially with respect to the effect of old age on the prefrontal cortex.

Component processes in task switching.

Participants switched between two randomly ordered, two-choice reaction-time (RT) tasks, where an instructional cue preceded the target stimulus and indicated which task to execute. Task-switching cost dissipated passively while the participants waited for the instructional cue in order to know which task to execute (during the Response-Cue Interval). Switching cost was sharply reduced, but not abolished, when the participants actively prepared for the task switch in response to the instructional cue (during the Cue-Target Interval). The preparation for a task switch has shown not to be a by-product of general preparation by phasic alertness or predicting target onset. It is suggested that task-switching cost has at least three components reflecting (1) the passive dissipation of the previous task set, (2) the preparation of the new task set, and (3) a residual component.

Modeling cognitive control in task-switching.

This article describes a quantitative model, which suggests what the underlying mechanisms of cognitive control in a particular task-switching paradigm are, with relevance to task-switching performance in general. It is suggested that participants dynamically control response accuracy by selective attention, in the particular paradigm being used, by controlling stimulus representation. They are less efficient in dynamically controlling response representation. The model fits reasonably well the pattern of reaction time results concerning task switching, congruency, cue-target interval and response-repetition in a mixed task condition, as well as the differences between mixed task and pure task conditions.

Task set switching in schizophrenia.

The authors used a task-switching paradigm to investigate set shifting ability in schizophrenia. This paradigm included 2 choice reaction time (RT) tasks: up-down and right-left. Switching tasks were associated with costs (i.e., longer RT in task-switch trials than in task-repetition trials); patients responded more slowly than controls and suffered greater switching costs, were as efficient as controls in engaging in an upcoming task set, and were faster than controls in disengaging from the previous task set. There were indications that patients quickly forgot what each keypress indicated, making it necessary for them to acquire response meaning information anew in each trial. To test this notion, the authors subsequently tested normal participants in conditions in which response meaning information needed to be acquired anew in each trial. These participants produced a pattern of switching costs resembling that of patients. Results suggest that set switching difficulties in schizophrenia, as exhibited in the present paradigm, reflect poor memory for task context information.

On the interaction between linguistic and pictorial systems in the absence of semantic mediation: evidence from a priming paradigm.

Use of the letter search task in the context of the priming paradigm has proved to be an invaluable tool for the investigation of the strategic control of processes involved in word recognition. In particular, previous findings that letter search on a prime word interferes with the priming of semantically/associatively related targets, but not with the priming of either identical or morphologically related targets, suggests that letter search may selectively interfere with semantic processing, leaving other levels of processing intact. In the present experiments, this investigation was extended by exploring the priming of pictures following letter search of either a same-concept word (repetition priming) or a semantically/associatively related word (semantic priming). There was significant repetition priming of picture categorization following both silent reading and letter search of the prime word (Experiments 1 and 2). In contrast, semantic priming of pictures was found only following silent reading of the prime; there was no semantic priming following letter search of the prime (Experiment 2). This pattern of results suggests that focusing attention at the letter level during prime processing selectively attenuates activation of the semantic system by the prime. It does not prevent the spread of activation between the lexical and pictogen levels of representation of a given concept.

Do long tests yield a more accurate diagnosis of dementia than short tests? A comparison of 5 neuropsychological tests.

OBJECTIVE: To provide comparative evidence for a valid and practical measure of mental-status functioning that could be used in dementia clinics. DESIGN: Five mental-status neuropsychological tools for dementia screening were administered to patients in a memory disorder clinic. These included the Mini-Mental State Examination, the Dementia Rating Scale, the 6-item derivative of the Orientation-Memory-Concentration Test, a short Mental Status Questionnaire, and a composite tool we labeled the Ottawa Mental Status Examination, which assessed orientation, memory, attention, language, and visual-constructive functioning. The tools were compared using various criteria, including the statistical factors of sensitivity and reliability; effects of gender, native language, and language of testing; the utility of these tests for the differential diagnosis of Alzheimer-type and vascular dementia; and sensitivity to cognitive decline in the entire sample and among patients with severe dementia. RESULTS: All of the tests were highly intercorrelated, suggesting that they are interchangeable. CONCLUSION: The comparisons along the various criteria indicate that if the objective is to have a general index of dementia of the Alzheimer type, short tests are at least as good and sometimes better than the longer tests.

Diagnosis of dementia. Methods for interpretation of scores of 5 neuropsychological tests.

OBJECTIVE: To provide methods to interpret and compare different neurobehavioral screening tests for the diagnosis of dementia. DESIGN: Five mental-status neuropsychological tools for dementia screening were administered to patients in a memory disorder clinic. These included the Mini-Mental State Examination, the Dementia Rating Scale, the 6-item derivative of the Orientation-memory-Concentration Test, a short Mental Status Questionnaire, and a composite tool we labeled the Ottawa Mental Status Examination, which assessed orientation, memory, attention, language, and visual-constructive functioning. RESULTS: To obtain z and percentile scores, norms are for the different tests, computed separately for patients with dementia of the Alzheimer type, vascular dementia, or no dementia. Another set of norms is reported in which a test score is translated directly into the posttest probability of dementia. Translation formulas are given to allow the estimation of the score on one test from the result on another test. CONCLUSION: The interpretation of tests used to diagnose dementia must be based on an understanding of the meaning of an individual score, which is based on the question asked and the population to which the patient is referenced.

Is reading ability related to activation dumping speed? Evidence from immediate repetition priming.

In parallel processing models, residual activity constitutes noise that must be dumped, and fast dumping is associated with efficient processing. Subjects performed a continuous lexical decision task with repetitions (Experiments 1 and 2). Efficient readers (who had high comprehension and vocabulary scores) showed smaller repetition priming than did inefficient readers, but mostly at Lag 0 (equivalent to 3-sec stimulus onset asynchrony [SOA]). Experiment 3 manipulated the empty inter-repetition interval. It was found that reading ability was negatively related to repetition priming mostly when the SOA was 3 sec, but less so when it was 2 or 4 sec. Experiment 4 failed to find similar reading ability differences when the task was continuous recognition. The findings are interpreted as showing that efficient readers managed to dump residual activity related to subsemantic information in less than 3 sec, whereas inefficient readers required 3-4 sec.

Dissociation of processes underlying spatial s-r compatibility: evidence for the independent influence of what and where.

The process-dissociation procedure was used to estimate the influence of spatial and form-based processing in the Simon task. Subjects made manual (left/right) responses to the direction of arrows (> or <) presented to the left or right of fixation. Manipulating the proportion of incongruent trials (e.g., a right-pointing arrow presented to the left of fixation) affected both the size and direction of the Simon effect. To account for this pattern of data, we compared process estimates based on three possible relationships between spatial and form-based processing: independence, redundancy, and exclusivity. The independence model provided the best account of the data. Most telling was that independent form-based estimates were superior at predicting observed performance on arrows presented at fixation and did so consistently across conditions (r's > .80). The results provide evidence that the form ("what") and spatial location ("where") of a single stimulus can have functionally independent effects on performance. They also indicate the existence of two kinds of automaticity--an associative ("implicit learning") component that reflects prior S-R mappings and a nonassociative component that reflects the correspondence between stimulus and response codes.

The role of attention in illusory conjunctions.

In five experiments, we investigated the effects of attention on illusory conjunctions formed between features of unrelated objects. The first three experiments used a weak manipulation of attention and found that illusory conjunctions formed either among features receiving high attentional priority or among features receiving low attentional priority were not more frequent than were conjunctions formed between mixed features of different attentional priority. The last two experiments used a strong manipulation of attention and failed to reveal any evidence of true illusory conjunctions. The results are inconsistent with the feature-integration theory, which predicts that when attention is focused on a subset of items, illusory conjunctions ought to occur within and outside of the attended subset, but not between the attended and unattended items.