Implicit and explicit conceptual memory following frontal lobe damage.

In two experiments, the performance of patients with frontal lobe lesions was examined on implicit and explicit tests of conceptual memory for organized lists of words. Frontal patients exhibited normal levels of conceptual priming on implicit category production and free association tests, but they exhibited impaired memory performance on explicit category- and associate-cued recall tests. The findings of normal performance on implicit conceptual tests suggest that frontal patients do not have a basic deficit in semantic processing of individual items. Impaired performance on explicit cued recall tests may be related to deficits in the use of organizational encoding and strategic retrieval processes.

Response channel activation and the lateral prefrontal cortex.

The role of lateral prefrontal cortex in transducing perception into action was studied in 10 patients with chronic, unilateral lesions. They identified colors in the center of a visual display, while a flanking, distractor color was presented simultaneously in either the ipsilesional or contralesional field. The flanker could be either the same color as the target, or incompatible with the correct response. The effects of compatible and incompatible flankers on reaction time (RT) served as a measure of response channel activation by the flanker. Flankers in the contralesional field influenced RT less than did those in the ipsilesional field. These results suggest that the lateral prefrontal cortex is involved in maintaining stimulus-response channels.

Impaired use of organizational strategies in free recall following frontal lobe damage.

Free recall, use of organizational strategies, and interference effects were assessed in patients with frontal lobe lesions and control subjects. In three experiments, patients with frontal lobe lesions exhibited impaired free recall and reduced use of organizational strategies in tests of memory. Reduced use of strategies was observed on tests of recall of unrelated items, as measured by subjective organization, and on tests of recall of related items, as measured by both category clustering and subjective organization. Frontal patients benefited from strategy instruction at either study or test, suggesting that both encoding and retrieval processes are impaired by frontal lobe damage. These findings indicate that the free recall impairments exhibited by patients with frontal lobe lesions may be caused at least in part by deficits in the use of organizational strategies. In addition, when first-list learning was matched for patients and control subjects, patients with frontal lobe lesions exhibited relatively increased sensitivity to proactive interference during second-list learning.

Semantic facutation in aphasia: effects of time and expectancy.

Abstract Two auditory lexical decision semantic priming experiments were conducted to examine the extent to which the automaticcontrolled processing dichotomy can characterize lexical access deficits in Broca's and Wernicke's aphasics. In Experiment 1, prime-target predictability was varied while the interval between prime and target (ISI) was held constant. In Experiment 2, ISI was varied while prime-target predictability was held constant. The pattern of semantic facilitation and inhibition results for Experiment 1 showed that Broca's aphasics were influenced by prime-target predictability, whereas Wernicke's aphasics were not. In contrast in hperiment 2, manipulations of ISI at 150 and 2000 msec did not affect patterns of semantic facilitation for either Broca's or Wernicke's aphasics. Taken together, the results of these two experiments suggest that Broca's aphasics use heuristic strategies more so than old and young normal subjects. In addition, they seem to have an automatic processing deficit affecting the level of activation of lexical entries, with a spared time course of activation. Wernicke's aphasics show a pattern of results consistent with the view that automatic processing is unimpaired in these patients, while they fail to use heuristic strategies in these tasks.

Susceptibility to Memory Interference Effects following Frontal Lobe Damage: Findings from Tests of Paired-Associate Learning.

Abstract Patients with frontal lobe lesions were adminstered tests of paired-associate learning in which cue and response words are manipulated to increase interference across two study lists. In one test of paired-associate learning (AB-AC test), cue words used in one list are repeated in a second list but are associated with different response words (e.g., LION-HUNTER, LION-CIRCUS). In another test (AB-ABr test), words used in one list are repeated in a second list but are rearranged to form new pairs. Compared to control subjects, patients with frontal lobe lesions exhibited disproportionate impairment of second-list learning as a result of interference effects. In particular, patients exhibited the poorest performance during the initial trial of the second list, a trial in which interference effects from the first list would be most apparent. These findings suggest that the on-line control of irrelevant or competing memory associations is disrupted following frontal lobe lesions. This disruption may be indicative of an impaired gating or filtering mechanism that affects not only memory function but other cognitive function as well.

Serial position effects in implicit and explicit tests of memory.

The effects of serial position at study on implicit and explicit tests of memory were investigated. Both primary and recency effects were observed in implicit tests of word-stem completion. These effects, however, were transient. No serial position effects were found in the second half of testing (Experiments 1 and 3) or when testing followed a 1-min, filled delay (Experiment 2). Serial position effects were also examined in explicit tests of cued recall. When performance on explicit cued recall was below ceiling levels, a primacy effect persisted throughout testing (Experiment 3). Similarly, in explicit tests of free recall, primacy effects were consistently observed, both with immediate testing (Experiments 1 and 3) and when testing followed a filled delay (Experiment 2).

Intact implicit memory in patients with frontal lobe lesions.

Patients with frontal lobe lesions and control subjects were administered tests of word-stem completion priming. In this implicit memory test, subjects are first presented words (e.g. MOTEL, PARADE) in an incidental learning paradigm. Following word presentation, subjects are shown word stems (e.g. MOT, PAR) and asked to produce the first word that comes to mind. Patients with frontal lobe lesions exhibited normal levels of word-stem completion. These findings indicate that implicit memory can operate normally despite damage to the prefrontal cortex. The present results substantiate previous neuropsychological and positron emission tomography findings which indicate that word priming depends critically on posterior cortical areas.

Syntactic priming effects in aphasia: an investigation of local syntactic dependencies.

This study explored on-line processing of local syntactic dependencies in normal subjects and in Broca's and Wernicke's aphasics using a lexical decision paradigm. In addition, subjects performed a grammatically judgement task on the real word pairs used in the lexical decision tasks. Results of two experiments for normal subjects indicated different syntactic priming effects as a function of the type of local syntactic dependency. Word pairs that formed a single constituent phrase, i.e., a verb phrase, showed both facilitory and inhibitory effects, whereas word pairs that reflected local syntactic dependencies across a phrase boundary, i.e., pronoun verb, showed only inhibitory effects. Broca's aphasics failed to show facilitory effects when presented with word pairs forming a single constituent phrase but, similar to normals, did show inhibition when presented with word pairs that reflected local syntactic dependencies across a phrase boundary. In contrast, Wernicke's aphasics failed to show inhibitory effects in both experiments. The implications of these results for theories of language processing deficits in aphasia are considered.