Verbal and design fluency in patients with frontal lobe lesions.

The ability to generate items belonging to categories in verbal fluency tasks has been attributed to frontal cortex. Nonverbal fluency (e.g., design fluency) has been assessed separately and found to rely on the right hemisphere or right frontal cortex. The current study assessed both verbal and nonverbal fluency in a single group of patients with focal, frontal lobe lesions and age- and education-matched control participants. In the verbal fluency task, participants generated items belonging to both letter cues (F, A, and S) and category cues (animals and boys' names). In the design fluency task, participants generated novel designs by connecting dot arrays with 4 straight lines. A switching condition was included in both verbal and design fluency tasks and required participants to switch back and forth between different sets (e.g., between naming fruits and furniture). As a group, patients with frontal lobe lesions were impaired, compared to control participants, on both verbal and design fluency tasks. Patients with left frontal lesions performed worse than patients with right frontal lesions on the verbal fluency task, but the 2 groups performed comparably on the design fluency task. Both patients and control participants were impacted similarly by the switching conditions. These results suggest that verbal fluency is more dependent on left frontal cortex, while nonverbal fluency tasks, such as design fluency, recruit both right and left frontal processes.

The Ponzo illusion and the perception of orientation.

A new theory, called the tilt constancy theory, claims that the Ponzo illusion is caused by the misperception of orientation induced by local visual cues. The theory relates the Ponzo illusion-along with the Zöllner, Poggendorff, Wündt-Hering, and cafe wall illusions-to the mechanisms that enable us to perceive stable orientations despite changes in retinal orientation or body orientation. In Experiment 1, the magnitude of the misperception of orientation was compared with the magnitude of the Ponzo illusion. In Experiment 2, predictions of the tilt constancy theory were compared with accounts based on (1) low spatial frequencies in the image, (2) memory comparisons (pool-and-store model), and (3) relative sizejudgments. In Experiment 3, predictions of the tilt constancy theory were tested against predictions of the assimilation theory of Pressey and his colleagues. In the final experiment, the orientation account was compared with theories based on linear perspective and inappropriate size constancy. The results support the tilt constancy theory.

Source memory enhancement for emotional words.

The influence of emotional stimuli on source memory was investigated by using emotionally valenced words. The words were colored blue or yellow (Experiment 1) or surrounded by a blue or yellow frame (Experiment 2). Participants were asked to associate the words with the colors. In both experiments, emotionally valenced words elicited enhanced free recall compared with nonvalenced words; however, recognition memory was not affected. Source memory for the associated color was also enhanced for emotional words, suggesting that even memory for contextual information is benefited by emotional stimuli. This effect was not due to the ease of semantic clustering of emotional words because semantically related words were not associated with enhanced source memory, despite enhanced recall (Experiment 3). It is suggested that enhancement resulted from facilitated arousal or attention, which may act to increase organization processes important for source memory.

Differential effects of cue dependency on item and source memory.

The authors investigated the cue dependency of source and item memory. Individuals listened to words spoken by a man or a woman and later determined whether a test word was previously presented by a man or by a woman, or whether it was a new word. Cue dependent effects were assessed by presenting test words with (a) the same voice (match condition) that originally presented the word, (b) a different but familiar voice (mismatch condition), (c) a novel test voice (novel condition), and (d) no test voice (control condition). Compared with the control condition, source recollection was facilitated in matching-context conditions, disrupted in mismatching-context conditions, and not affected in novel test conditions. By contrast, item recognition was not affected by the match-mismatch manipulation but was significantly worse in novel test voice conditions. The authors propose an associative source interference view to account for the voice match-mismatch effects observed in source recollection.

Toward a cognitive neuroscience of metacognition.

The relationship between metacognition and executive control is explored. According to an analysis by Fernandez-Duque, Baird, and Posner (this issue), metacognitive regulation involves attention, conflict resolution, error correction, inhibitory control, and emotional regulation. These aspects of metacognition are presumed to be mediated by a neural circuit involving midfrontal brain regions. An evaluation of the proposal by Fernandez-Duque et al. is made, and it is suggested that there is considerable convergence of issues associated with metacognition, executive control, working memory, and frontal lobe function. By integrating these domains and issues, significant progress could be made toward a cognitive neuroscience of metacognition.

An analysis of signal detection and threshold models of source memory.

The authors analyzed source memory performance with an unequal-variance signal detection theory model and compared the findings with extant threshold (multinomial and dual-process) models. In 3 experiments, receiver operating characteristic (ROC) analyses of source discrimination revealed curvilinear functions, supporting the relative superiority of a continuous signal detection model when compared with a threshold model. This result has implications for both multinomial and dual-process models, both of which assume linear ROCs in their description of source memory performance.

Retrieval-induced forgetting in episodic memory.

Participants learned the locations of 12 stimuli that were uniquely colored but could be grouped by shape (4 circles, 4 triangles, 4 crosses). Following the study, a retrieval-practice phase required participants to recall the colors of a subset of the stimuli (i.e., 2 circles, 2 triangles) using shape and location as cues. In a final test, participants recalled the colors of all 12 stimuli. Compared with the control set of stimuli (i.e., 4 crosses), memory was facilitated for practiced items but impaired for related items, which were not practiced but shared the same shape group. Across experiments, retrieval-induced forgetting was observed for different perceptual groupings and for different cuing procedures. The effect, however, required retrieval of information during the interpolated phase. Providing extra presentations did not disrupt memory for related items.

Monitoring item and source information: evidence for a negative generation effect in source memory.

Item memory and source memory were assessed in a task that simulated a social conversation. Participants generated answers to questions or read statements presented by one of three sources (faces on a computer screen). Positive generation effects were observed for item memory. That is, participants remembered topics of conversation better if they were asked questions about the topics than if they simply read statements about topics. However, a negative generation effect occurred for source memory. That is, remembering the source of some information was disrupted if participants were required to answer questions pertaining to that information. These findings support the notion that item and source memory are mediated, as least in part, by different processes during encoding.

On the recollection of specific- and partial-source information.

Memory judgments can be based on information that is more or less specific with respect to the source of an item. The authors introduce a procedure and multinomial model for measuring specific- and partial-source information. In 2 experiments, participants heard words spoken by 4 different voices: 2 male voices and 2 female voices. During the test, participants were required to remember who spoke the test items (e.g., Male 1, Male 2, Female 1, Female 2, or new word). Participants often remembered information about the gender of the source (i.e., partial-source information) when they did not remember information that identified the source itself (i.e., specific-source information). Dividing attention during retrieval impaired participants' memory for specific-source information (i.e., voice information) but did not affect memory for partial-source information (i.e., gender information).

Mapping symbols to response modalities: interference effects on Stroop-like tasks.

Response compatibility effects were assessed with a Stroop-like task which involved arrow and word stimuli. The subjects were required to respond to one stimulus--an arrow (e.g.,-->) or a word (e.g., left)--and ignore the other. It was shown that response compatibility played a significant role in generating Stroop-like interference. Robust interference effects were observed when the subjects responded manually to word stimuli (ignoring irrelevant arrows) and when they responded vocally to arrow stimuli (ignoring irrelevant words). Smaller interference effects were observed under response-compatible conditions, namely, responding manually to arrows and vocally to words. In the second experiment, within-dimension displays (e.g., arrow-arrow or word-word displays) yielded a pattern of interference that did not interact with response modality. These findings indicate that both stimulus-response compatibility effects and target-distractor similarity are crucial for understanding Stroop-like interference.

Letter and category fluency in patients with frontal lobe lesions.

This study examines the hypothesis that patients with frontal lobe lesions are impaired on tests of letter but not category fluency. This hypothesis was proposed by Moscovitch (1994), based on a series of cognitive studies with young, normal participants. A group of patients with lateral prefrontal lesions and age-matched controls were tested on 2 tests of verbal fluency, the FAS task and a category fluency task that used semantic categories as cues (e.g., animals). Patients with frontal lobe lesions generated fewer items than controls on both letter and category fluency. This effect did not interact with the type of fluency test, suggesting that the frontal lobes are more generally involved in verbal fluency. Moreover, this pattern of findings, along with previous results of impaired free recall and remote retrieval in this patient group, suggests that patients with frontal lobe lesions do not efficiently organize and develop retrieval strategies.

Impaired word-stem priming in patients with temporal-occipital lesions.

In the word-stem priming test, words are presented (e.g., MOTEL, PARADE), and later subjects are shown three-letter word stems (e.g., MOT, PAR) and asked to complete each stem with the first word that comes to mind. Word-stem priming, as well as other aspects of implicit memory, are intact in amnesic patients with medial temporal lesions. However, this form of priming has been shown to be impaired in patients with Alzheimer's disease, suggesting that damage to neocortical areas outside the medial temporal lobe contributes to impaired priming in these patients. To examine the role of posterior cortical areas on word-stem priming, we administered the test to patients with unilateral temporal-occipital lesions. Patients with temporal-occipital lesions exhibited significantly impaired priming on this test. The findings suggest a critical role of the inferior posterior neocortex in the expression of this form of implicit memory.

Functional Neuroimaging of Cortical Dysfunction in Alcoholic Korsakoff's Syndrome.

Many neuropsychological investigations of human memory have focused on the amnesic deficits of alcoholic Korsakoff's syndrome. Structural neuroimaging suggests that the syndrome results from midline diencephalic damage, but functional neuroimaging has the potential to reveal additional neuropathology that may be responsible for cognitive dysfunction. Accordingly, high-resolution positron emission tomography (PET) was used to measure regional cerebral metabolic rates for glucose utilization in five alcoholic Korsakoff patients and nine alcoholic control subjects. Results from a continuous recognition test administered during the radiotracer uptake period indicated that all subjects performed normally with respect to immediate memory, whereas Korsakoff patients demonstrated a marked memory impairment in delayed recognition. PET results from the Korsakoff group showed a widespread decline in glucose metabolism in frontal, parietal, and cingulate regions, suggesting that these functional abnormalities in the cerebral cortex contribute to the memory impairment. Hippocampal glucose metabolism did not differ between the groups. Thus, the evidence did not support the hypothesis that parallel brain dysfunctions are responsible for the similar amnesic symptomatology after hippocampal and diencephalic damage. We hypothesize that the amnesic dysfunction of Korsakoff's syndrome depends on a disruption of thalamocortical interactions that mediate a function critical for normal memory storage.

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.

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).

Cognitive neuropsychology is more than single-case studies.

S. M. Sokol et al. (1991) claim that "The Cognitive Neuropsychology Approach" (p. 355) is limited to the single-case study design. The present article takes issue with this claim. Contrary to the beliefs of Sokol et al., we argue (a) that cognitive modularity is best studied by group design, (b) that the possibility of neural reorganization in patients should be tested through converging evidence from different populations using various methods, and (c) that cognitive neuropsychology can benefit from being a part of cognitive neuroscience where both neural and cognitive mechanisms underlying normal cognition are relevant.

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.

On the relationship between recall and recognition memory.

The relationship between recall and recognition has been a central topic for the study of memory. A test of alternative views about recall and recognition was arranged by studying amnesic patients. In amnesia, damage has occurred to a brain system important for declarative (conscious) memory, but skill learning, priming, and other forms of nonconscious memory are intact. Recall and recognition were found to be proportionately impaired in amnesic patients, and confidence ratings for the recognition judgments were commensurate with the level of impaired performance. The results are contrary to views that either recognition memory or associated confidence judgments are ordinarily supported significantly by nonconscious memory. The results favor the view that recall and recognition are related functions of declarative memory and equivalently dependent on the brain system damaged in amnesia.