Output and retrieval interference in the missing-number task

Three experiments are reported that represent a reexamination of the missing-number method (Buschke, 1963b) of estimating short-term memory span. The missing-number task involved presenting a random sequence of all but one of the numbers of a known reference set and asking subjects to identify the missing number. Experiment 1 introduced a modified missing-number task that included two missing items and two choices made by the subject. With a large decline in performance for the second choice relative to the first, it is possible that only the second choice was subject to output or retrieval interference. An alternative explanation is that subjects output the number with the weakest memory representation as their first response. By postcuing subjects to report their two choices in a forward or backward sequence, Experiment 2 provided evidence against the importance of output interference and support either for the importance of retrieval interference or for the "weakest-first" hypothesis. However, with a paradigm that replaced only correctly identified missing numbers, a prediction that subjects would select the number with the weakest memory representation as their first response was not confirmed in Experiment 3. Instead, retrieval interference was implicated to explain the first-choice superiority found in Experiments 1 and 3. The results were interpreted in terms of the TODAM model of Murdock (1982, 1987, in press).     

Effects of preliminary perceptual output on neuronal activity of the primary motor cortex.

Observations of single neurons in the primary motor cortex of 1 monkey provided evidence that preliminary perceptual information reaches the motor system before perceptual analysis is complete. Neurons were recorded during a task in which 1 stimulus was assigned to a wrist flexion response and another was assigned to wrist extension. Two stimuli were assigned to a no-go response; each was visually similar to either the flexion or the extension stimulus. When a no-go stimulus was presented, neurons responded with weaker versions of the discharge patterns exhibited to the visually similar stimulus requiring a movement, suggesting that neurons receive partial perceptual information favoring that movement. Functionally separable neuronal populations were identified, and differences in the activations of these provide evidence about the functional effects of preliminary perceptual output on movement control processes.     

Musical duplex perception: perception of figurally good chords with subliminal distinguishing tones.

In a variant of duplex perception with speech, phoneme perception is maintained when distinguishing components are presented below intensities required for separate detection, forming the basis for the claim that a phonetic module takes precedence over nonspeech processing. This finding is replicated with music chords (C major and minor) created by mixing a piano fifth with a sinusoidal distinguishing tone (E or E flat). Individual threshold intensities for detecting E or E flat in the context of the fixed piano tones are established. Chord discrimination thresholds defined by distinguishing tone intensity were determined. Experiment 2 verified masked detection thresholds and subliminal chord identification for experienced musicians. Accurate chord perception was maintained at distinguishing tone intensities nearly 20 dB below the threshold for separate detection. Speech and music findings are argued to demonstrate general perceptual principles.     

Temporary suppression of visual processing in an RSVP task: an attentional blink? .

Through rapid serial visual presentation (RSVP), we asked Ss to identify a partially specified letter (target) and then to detect the presence or absence of a fully specified letter (probe). Whereas targets are accurately identified, probes are poorly detected when they are presented during a 270-ms interval beginning 180 ms after the target. Probes presented immediately after the target or later in the RSVP stream are accurately detected. This temporary reduction in probe detection was not found in conditions in which a brief blank interval followed the target or Ss were not required to identify the target. The data suggest that the presentation of stimuli after the target but before target-identification processes are complete produces interference at a letter-recognition stage. This interference may cause the temporary suppression of visual attention mechanisms observed in the present study.     

On the transmission of partial information: inferences from movement-related brain potentials.

Results are reported from a new paradigm that uses movement-related brain potentials to detect response preparation based on partial information. The paradigm uses a hybrid choice-reaction go/nogo procedure in which decisions about response hand and whether to respond are based on separate stimulus attributes. A lateral asymmetry in the movement-related brain potential was found on nogo trials without overt movement. The direction of this asymmetry depended primarily on the signaled response hand rather than on properties of the stimulus. When the asymmetry first appeared was influenced by the time required to select the signaled hand, and when it began to differ on go and nogo trials was influenced by the time to decide whether to respond. These findings indicate that both stimulus attributes were processed in parallel and that the asymmetry reflected preparation of the response hand that began before the go/nogo decision was completed.     

Automatic and attentional priming in young and older adults: reevaluation of the two-process model.

Three experiments addressed the distinction between automatic and attentional mechanisms underlying semantic priming effects by factorially crossing prime-target relatedness, expectancy, and SOA in a task (pronunciation) that minimized postlexical checking processes. Also, possible age-related (young vs. older adults) differences in the automatic and attentional mechanisms were addressed. Across all experiments there was evidence of a Relatedness x Expectancy x SOA interaction, which is inconsistent with the notion of independent automatic and attentional mechanisms in semantic priming and the notion of a self-encapsulated modular lexicon. The results also indicated age-related differences in the build-up of the expectancy effect across SOAs when the prime was visually available for only 200 ms, independently of the prime-target SOA (Experiments 1 and 3), but not when the prime was visually available throughout the SOA (Experiment 2).     

Rapid Automatized Naming and gesture by normal and language-impaired children

This study investigates whether language-impaired (LI) children show deficits in rapid automatized naming and whether RAN performance is specific to verbal output (or to rapid motor output in general). A total of 67 LI and 54 age-matched control children were tested with the Rapid Automatized Naming (RAN) test (Denckla & Rudel, 1976) and with a manual version of the RAN (RAN-manual) in which subjects were required to provide a nonverbal, pantomime response. Subjects also completed tests of rapid oral and manual sequencing skills and standardized tests of reading ability. Each subject was tested at 4, 6, and 8 years old. The results showed that LI children perform significantly poorer on both versions of the RAN than age-matched controls. Correlations between RAN scores and tests of reading ability were significant for normal and LI subjects and were particularly high for 8-year-old LI children. RAN-manual scores also correlated with 8-year-old LI children's reading scores. Further, RAN and RAN-manual scores for the LI children correlated significantly with these children's manual sequencing abilities, whereas this was not the case for the control subjects. These findings suggest that LI children's rapid sequential processing deficits are not limited to verbal output, but also generalize to other motoric domains.     

Morphologic agrammatism following a right hemisphere stroke in a dextral patient.

There is evidence of two major components of grammatic function in the brain: (1) morphologic, probably based in the postcentral perisylvian cortex, encompassing the selection of individual words and inflectional endings according to the rules of grammar; and (2) syntactic, probably based in the frontal lobes, encompassing construction of the overall structure of a sentence (syntax) to match the concept being considered. We present a stroke patient with impaired morphology but, unlike Broca's aphasics, relative sparing of syntax. He omitted 43% of articles, 40% of complementizers, 20% of pronouns, 27% of semantically marked prepositions, 43% of purely grammatic prepositions, and 22% of auxiliary verbs, but his average sentence length was 9.8 words and 64% of his sentences contained embedded clauses. He frequently intermingled two sentences to convey a given concept, juxtaposing words in grammatically unacceptable ways. This intermingling may represent either a grammatic "conduite d'approche," or a failure of the filtering function of a defective morphologic processor. His great difficulty in completing syntactic frames suggests that a more general form of the processes underlying grammatic morphology may play an important role in phrase structure generation.     

The usefulness of the Western Aphasia Battery for differential diagnosis of Alzheimer dementia and focal stroke syndromes: preliminary evidence.

We assessed the usefulness of the Western Aphasia Battery for distinguishing the language disturbances caused by Alzheimer dementia (AD) from those caused by stroke. Using discriminant function analyses, the multiple variable "aphasia quotient--reading quotient--writing quotient" classified 29 (72.5%) of the 40 patients correctly. These 29 patients included 8 of 10 patients with left hemisphere infarction and fluent aphasia; 6 of 10 with AD; 5 of 10 patients with right hemisphere infarction; and all 10 of the neurologically normal control subjects. The patients with AD and those with right hemisphere stroke were the most difficult to classify using the aphasia battery.