Shifting attention to different levels within global-local stimuli: A study of normal participants and a patient with temporal-parietal lobe damage.

Shifts of attention to different levels of global-local stimuli were examined in normal participants and a patient with right temporal-parietal lobe damage. Global-local stimuli were presented in sequential couplets and the target could either be at the same global-local level or the target could change levels within each couplet. Normal participants were faster to respond to the second stimulus when the target remained at the same level compared to when it changed levels. This level-shifting effect appeared to be independent of any perceptual- or identity/response-based priming, and did not appear to be due to the size of the stimuli per se. In contrast, the patient did not display any level-shifting effects when the target appeared at the global level, whereas he did display this effect when the target appeared at the local level. These results suggest that the right temporal-parietal lobe may be involved in activating attentional weights to the different levels of global-local stimuli. These results also indicate that intra-stimulus attentional shifts are mediated by different neurocognitive mechanisms than are spatial attentional shifts.

Spatial attention deficits in humans: a comparison of superior parietal and temporal-parietal junction lesions.

Although clinical evidence of spatial attention deficits, such as neglect and extinction, is typically associated with lesions of the right temporal-parietal junction, recent evidence has suggested an important role for the superior parietal lobe. Two groups of patients, selected for lesions at the temporal-parietal junction including the superior temporal gyrus (TPJ group), or for lesions involving the parietal but not the superior temporal region (PAR group), performed cued-target detection tasks in 2 experiments. An extinction-like response time pattern was found for the TPJ but not the PAR group. In addition, both groups were able to use expectancy information, in the form of cue predictiveness, suggesting that separate mechanisms mediate exogenous and endogenous processes during attention shifts.

Lexical priming by pictures and words in normal aging and in dementia of the Alzheimer's type.

Alzheimer's disease causes a progressive loss of semantic memory, one manifestation of which is a progressive language deficit. In order to delineate the relationship between cognitive processing deficits and language disturbance, word-word and picture-word lexical-decision priming tasks were administered to patients with mild dementia of the Alzheimer's type (DAT) (n = 6), very mild DATs (n = 7), and older normals (n = 23). The mild DATs differed from the other two groups in both tasks. When pictures were used as primes, significant identity priming was seen in the normals and very mild DATs, but not in the mild DATs. The mild DATs showed an aberrant pattern-responses significantly slower with picture primes than with nonsense primes in all three picture-word conditions. This may reflect residual inhibitory activity within a damaged associational network. In the word-word paradigm, the mild DAT subjects demonstrated significant priming both when the prime and target were identical (identity priming, e.g., dog-dog) and when they were semantically related (semantic priming, e.g., cat-dog). The other two groups showed no significant priming. These data reinforce other studies which have found that DAT subjects show a supranormal amount of word-word lexical-decision priming. This "hyperpriming" may occur due to partially degraded internal representations which benefit from priming more than intact representations (a cognitive crutch). Both paradigms thus exposed information-processing deficits which distinguished mild DATs from the other two groups. DAT-induced changes in selective attention are probably contributing to these results.

Capacity demands of automatic processes in semantic priming.

In three experiments, we examined the effects of prime-target stimulus onset asynchrony (SOA) and the proportion of related primes and targets (relatedness proportion, or RP) on semantic priming when the prime was either named or was searched for a specific letter. In Experiment 1, with an RP of .50, priming occurred at SOAs of 240 and 840 msec when the prime was named, but no priming was found at either SOA when the prime was searched for a letter. In Experiment 2 the RP was either .20 or .80, and the SOA was set at 1,700 msec; priming again was found in both conditions when the prime was named, but only in the RP .80 condition when a letter search task was performed on the prime. In Experiment 3, both the proportion of related trials and SOA were varied; as in the previous experiments, no priming effects were found with the letter search task for either SOA in the RP .20 condition, but the priming effect was reinstated in the RP .80 condition. These results are discussed with respect to how limited capacity resources are allocated and how they influence semantic priming effects.

Dissociation of lexical and semantic aspects in word processing.

We present data and review studies that show a dissociation between identity and semantic priming. This dissociation appears as a result of employing certain prime tasks, adding cognitive load or following brain damage. Such a dissociation suggests that while activation of the word's representation is obligatory, the spread of activation to related concepts is not.

Behavioral and computational models of spatial attention.

Pigeons pecked for food in a spatially cued choice reaction time (RT) task. A brief (50-ms) white light appeared on a left or right key and probabilistically predicted the location (on either the left or right key) of a subsequent target stimulus. The time between cue and target onset (stimulus onset asynchrony), the base rate of left cues, and the probability that the cue correctly predicted the target (cue validity) were experimentally varied. The mean RT to respond to the target key was faster on correctly cued trials (defining a validity effect), decreased for both valid and invalid trials as stimulus onset asynchrony increased (defining an alerting effect), showed a variety of base-rate effects, and did not depend on cue validity. It is shown with a computational-processing model that dynamic interactions of short-term and associative memory processes are sufficient to produce these attentionlike empirical phenomena.

Automatic processes in lexical access and spreading activation.

The semantic priming effect can be reduced or eliminated depending on how the prime word is processed. The experiments reported here investigate this prime task effect. Two experiments used identity and semantic priming tasks to determine whether the prime word is encoded at a lexical level under letter-search conditions. When the prime task was naming, both identity and semantic priming occurred; however, when a letter-search task was performed on the prime word, only identity priming occurred, thus supporting the argument that the search task affects activation of semantic associates rather than lexical access of the prime word. Another experiment demonstrated that this identity priming was the result of lexical processes rather than of letter-by-letter priming. A cross-modal priming technique demonstrated that the letter-search prime task does not actively suppress activation of semantic associates. The implications of these results for automaticity and for proposed mechanisms of priming are discussed.

Dysnomia in dementia and in stroke patients: different underlying cognitive deficits.

The performance of 11 Alzheimer's (DAT) and 8 anomic aphasic stroke patients is contrasted with that of 32 normal elderly subjects on both the Boston Naming Test (BNT) and the Controlled Oral Word Association Test (COW), a letter-category verbal-fluency test. While both tests require phonological processing, only the BNT requires semantic processing (object recognition). Both DAT and anomic aphasic stroke patients were significantly impaired on the BNT, with mean z scores (based on the performance of the normals) of -4.08 and -2.57, respectively; the DAT patients were significantly farther from normal than were the anomic aphasics. Their relative levels of impairment on the COW were reversed: The anomic aphasics' performance (z = 1.79) was worse than that of the DATs (z = -0.66). This pattern of performance on the two tests is consistent with the hypothesis that impaired word finding reflects impaired processing mainly of semantic information for the DAT subjects, mainly of lexical-phonological information for the anomic aphasic subjects.

Cognition and the basal ganglia. Separating mental and motor components of performance in Parkinson's disease.

Central to the concept of subcortical dementia is the implication that the increased response latencies, which distinguish the syndrome, are due to a slowing of thought processes. The term 'bradyphrenia' has been applied to this presumed slowing of thought in Parkinson's disease and implies (1) that increased response latencies are not strictly motoric but are due to slowed information processing, and (2) that the mental slowing is analogous to the bradykinesia observed in the motor domain and, hence, attributable to dysfunction of dopaminergic basal ganglia mechanisms. The current study attempts to validate this definition of bradyphrenia by seeking a slowing of thought in Parkinson's disease which can be linked directly to bradykinesia. Six parkinsonian patients with end-of-dose akinesia were studied in three experiments which allowed separation of the speed of specific cognitive operations from the speed of motor responses. Serving as their own controls, they were tested both during the parkinsonian 'off' state, and when bradykinesia was alleviated by drug therapy. Four additional patients with newly diagnosed Parkinson's disease were studied before and following successful treatment with L-DOPA/carbidopa. The first experiment measured the rate of memory scanning, the second examined orientating of attention in the visual fields, and the third measured the time required to prepare a manual movement. The results show that overall reaction time increased when patients were in the untreated state, but without a concomitant slowing of purely cognitive components. The slowing of thought often reported in Parkinson's disease does not necessarily accompany bradykinesia and thus may not be related to dopaminergic dysfunction. These findings emphasize the need for caution in inferring a slowing of thought from increased response latencies in subcortical disorders.

Interruption of phonological coding in conduction aphasia.

A case study of conduction aphasia, investigating single word repetition, phonological coding, and short-term memory, is reported. Evidence from intact adults suggests that repetition can occur through either a lexical route or a direct auditory-articulatory link. For this conduction aphasic, E.A., the direct link was impaired, although the lexical route could be used to produce accurate single word repetition. Several experiments demonstrated a significant impairment in the generation and maintenance of an abstract phonological code. The consequences of a disruption of phonological coding on speech perception and on verbal short-term memory are discussed.

Effects of parietal injury on covert orienting of attention.

The cognitive act of shifting attention from one place in the visual field to another can be accomplished covertly without muscular changes. The act can be viewed in terms of three internal mental operations: disengagement of attention from its current focus, moving attention to the target, and engagement of the target. Our results show that damage to the parietal lobe produces a deficit in the disengage operation when the target is contralateral to the lesion. Effects may also be found on engagement with the target. The effects of brain injury on disengagement of attention seem to be unique to the parietal lobe and do not appear to occur with our frontal, midbrain, and temporal control series. These results confirm the close connection between parietal lobes and selective attention suggested by single cell recording. They indicate more specifically the role that parietal function has on attention and suggest one mechanism of the effects of parietal lesions reported in clinical neurology.