Chunking versus foraging search patterns by rats in the hierarchically baited radial maze

Rats were exposed to a radial maze containing six black smooth arms and six wire-grid-covered arms and a striped 'exit arm' in experiment 1. The probability of a black or grid arm being baited (5/6 vs 1/6) with sunflower seeds was associated with its proximal cue for some rats (the Relevant Arm Cue group) but not for others (the Irrelevant Arm Cue group). All rats could terminate a trial and receive a highly preferred morsel of apple by entering the exit arm only after having sampled all six seed-baited arms. Relevant Arm Cue rats usually chose some arms from the more densely baited set before choosing an arm from the less densely baited set and made fewer reentries than Irrelevant Arm Cue rats. Although such clustered, higher choice accuracy in the Relevant Arm Cue group corresponds to human clustered, better recall of verbal items from lists hierarchically organized by categories, these rats did not similarly exhaustively retrieve items (arm locations). That is, when required to terminate a trial by entering the 'exit' arm for an apple morsel after having sampled all seed-baited arms, both groups were equally unable to withhold making nonrewarded premature exits. This nonexhaustive foraging search pattern was maintained in the next two experiments in which the radial maze was reduced to three black and three grid arms along with the striped 'exit' arm and in which black and grid arm cues were paired with number of seeds (eight or one) in an arm for Relevant Arm Cue rats. Although Relevant Arm Cue rats displayed perfect clustering by entering all eight-seeded arms before a one-seeded arm, they made more premature exits and reentries into eight-seeded arms in experiment 2 or when forced to enter all eight-seeded arms in experiment 3 than did Irrelevant Arm Cue rats. These foraging tendencies prevent accurate estimations of the amount of information (i.e., arm locations) rats can 'chunk'. Electronic Publication     

Metalinguistic Awareness in Children: A Developmental Progression

The purpose of this study was to determine if a developmental order exists in the metalinguistic ability of children to make judgments about the form of language while simultaneously attending to a meaningful linguistic context. The stimulus material consisted of a short story into which 20 nonsense lexical items had been substituted. The 20 stimuli were comprised of phonotactically illegal and legal sequences of phonemes. In addition, the lexical items had been positioned to replace either structure or content words within the story. The participants were 90 Caucasian children who were divided into nine age groupings from 4;0 to 12;11. Baseline data were obtained from 10 adults. All subjects were required to respond to the audio-recorded stimuli by pressing a button whenever a nonsense item was perceived. The data were analyzed for both number of correct responses and reaction times. Results revealed a major shift in metalanguage ability occurring between 7 and 8 years of age. The 8- to 12-year-olds responded correctly to more items and at significantly faster rates than the 4- to 7-year-olds. The adults outperformed the children on all tasks, showing that metalanguage development continues beyond childhood.     

Why Do Conceptual Analysts Disagree?

The practice of a priori conceptual analysis requires that the concept being analyzed be available in the analyst's mind. The difficulties of analysis and the existence of disagreements among analysts are explained by distinguishing the implicit knowledge we have of these concepts from the explicit knowledge we seek. This view of disagreement assumes that those who disagree are typically attempting to analyze a single shared concept. In this paper, reasons are developed for replacing this guiding assumption with the alternative assumption that members of a conceptual community often have similar, but not identical, concepts. Adopting this alternative requires that we rethink the nature and aims of conceptual analysis.     

When two memories can and cannot be retrieved concurrently

We examined whether two memories can be retrieved concurrently from long-term memory. In Experiment 1, the subjects recalled words, either from two categories—alternating between the two—or from just one category. In Experiment 2, the subjects recalled two words belonging to either the same category or different categories, and the category prompts for these two responses appeared either simultaneously or successively. The results of both studies are consistent with the view that two items from different categories must be retrieved serially, whereas two items from the same category can be retrieved in parallel.     

Overlapping mental operations in serial performance with preview

Dual-task research has revealed a response-selection bottleneck: response selection cannot occur simultaneously in two different tasks, though perceptual processing may overlap response selection (Welford, 1952; Pashler & Johnston, 1989). In serial performance with preview, the same task is performed repeatedly, but stimuli are available well before response. Does the dual-task bottleneck limit the rate of responding in this situation, despite the fact that task set need not change? Four experiments examined manual responses to letters, varying stimulus preview. Preview increased RTs for the first response and reduced the subsequent inter-response intervals (IRIs). Preview also reduced the effect of visual intensity and response duration on IRIs, whereas effects of stimulus-response mapping variables were unchanged. These results indicate that the response-selection bottleneck limits serial performance, just as it limits concurrent performance of two unrelated tasks. This implies that the response-selection bottleneck is not caused by the need to switch task set.     

Divided attention: Storing and classifying briefly presented objects

Although in many studies divided attention has been examined by having people perform the same task (e.g., report or search) with a large number of objects, in few studies have people had to perform two logically independent tasks involving the same brief display. In two experiments, subjects saw 200-msec arrays of characters. In dual-task blocks, theyclassified the color of some or all of the items (making an immediate response) andstored the shape of some of the items for a later recognition test. There was not much mutual interference between classifying and storing per se. However, the tasks were by no means independent: there was substantial interference whendifferent objects from the array had to be stored for one task and classified for the other. The results confirm that wholly unrelated visual tasks depend on the same input-attention system and suggest that attending to an object for any purpose may entail storing a representation of it in visual short-term memory.     

Competitive behavior: A manifestation of motivation for ability comparison

Social comparison theory predicts that when the person is uncertain about the level of his ability, he may seek comparison information through competitive behavior. This derivation, however, has never been directly tested. An experiment is reported in which the level of the subject's uncertainty about his competence was manipulated and subsequent measures of his competitive motivation and behavior were obtained. The data indicate that higher levels of uncertainty do lead to higher levels of motivation and competition, but only under conditions that minimize threat to self-esteem.     

Aphasia type and aging

We analyzed the relationship between age and clinical type of aphasia in 167 right-handed men who had suffered cerebrovascular accidents. Patients with unequivocal diagnoses as Broca's, Wernicke's, anomic, conduction, and global aphasics were considered. The median age of the Broca's group (51 years old) was significantly lower than that of the total group (55.8 years old), while the median age of the Wernicke's group was significantly higher (63 years old). Moreover the incidence of Wernicke's aphasia increased steadily with age, while incidence of the other types of aphasia peaked in the sixth decade and then diminished with increasing age.     

Dichhaptic hand-order effects with verbal and nonverbal tactile stimulation

The palms of normal right-handed subjects were stimulated dichhaptically, i.e., with competing, bimanually presented tactile stimuli consisting of pairs of letters, pairs of digits, or pairs of line orientations. The subjects were required to identify both stimuli in a particular order, and order of report was compared between hands and across stimulus materials. Results indicated right-hand superiority for letters and left-hand superiority for lines; no hand differences occurred for digits. However, observed differences between hands appeared with second reports only, suggesting that measures of tactile storage are more sensitive to laterality differences than measures closer in time to actual stimulation.