Group aggregates and individual reliability: The case of verbal short-term memory

Two experiments examined the generalizability of the effects of word length and phonological similarity with visual and auditory presentation in immediate verbal serial ordered recall. In Experiment 1, data were collected from 251 adult volunteers drawn from a broad cross-section of the normal population. Word length and phonological similarity in both presentation modes significantly influenced the group means. However, 43% of the subjects failed to show at least one of the effects, and the likelihood that effects appeared was highly correlated with verbal memory span. In Experiment 2, 40 subjects of the original sample were retested, 20 of whom had failed to show one or more effects in Experiment 1. Whether or not an effect had appeared for individual subjects on the first test session was a poor predictor of whether the effect would appear on retest. Finally, an analysis of subject reports demonstrated that the patterns of experimental data could be accounted for in part by the strategies that subjects reported using, and the effect of strategy was independent of the effect of span. The implications of these findings for theories of verbal short-term memory are discussed.     

Minimum rank and minimum trace of covariance matrices

This paper considers some mathematical aspects of minimum trace factor analysis (MTFA). The uniqueness of an optimal point of MTFA is proved and necessary and sufficient conditions for a point x to be optimal are established. Finally, some results about the connection between MTFA and the classical minimum rank factor analysis will be presented.     

Just lying there, remembering: improving recall of prose in amnesic patients with mild cognitive impairment by minimising interference

The hallmark of amnesia is poor explicit long-term memory along with normal short-term memory. It is often stated that information encountered by amnesic patients is forgotten within 1 minute of presentation. However, previous work has not distinguished between forgetting as a function of time versus the interfering material occupying that time. We show that there is a marked benefit of reduced interference in amnesic patients with mild cognitive impairment (MCI), a condition that is characterised by anterograde amnesia in the absence of other neuropsychological deficits and carries an increased risk for Alzheimer's disease. The result suggests that long-term memory is encoded in these patients to a greater extent than had been realised but that their memory is highly vulnerable to interference.     

The Prospective and Retrospective Memory Questionnaire (PRMQ): Normative data and latent structure in a large non-clinical sample

The Prospective and Retrospective Memory Questionnaire (PRMQ; Smith, Della Sala, Logie, & Maylor, 2000) was developed to provide a self-report measure of prospective and retrospective memory slips in everyday life. It consists of sixteen items, eight asking about prospective memory failures, and eight concerning retrospective failures. The PRMQ was administered to a sample of the general adult population (N = 551) ranging in age between 17 and 94. Ten competing models of the latent structure of the PRMQ were derived from theoretical and empirical sources and were tested using confirmatory factor analysis. The model with the best fit had a tripartite structure and consisted of a general memory factor (all items loaded on this factor) plus orthogonal specific factors of prospective and retrospective memory. The reliabilities (internal consistency) of the Total scale and the Prospective and Retrospective scales were acceptable: Cronbach's alpha was 0.89, 0.84, and 0.80, respectively. Age and gender did not influence PRMQ scores, thereby simplifying the presentation and interpretation of normative data. To ease interpretation of scores on the PRMQ, tables are presented for conversion of raw scores on the Total scale and Prospective and Retrospective scales to T scores (confidence limits on scores are also provided). In addition, tables are provided to allow users to assess the reliability and abnormality of differences between an individual's scores on the Prospective and Retrospective scales.     

The role of memory in the Tower of London task

The Tower of London (TOL) task is widely used as a neuropsychological test of planning. Relatively little is known of the cognitive components of the task, and in particular the role of memory in performance. The current studies on normal adults looked at the role of verbal and spatial working memory in the TOL. The effects of verbal and visuospatial dual-task manipulations on TOL performance were examined in an experiment with 36 participants. Both verbal and visuospatial executive secondary tasks caused poorer performance on the TOL; however, concurrent articulatory suppression enhanced performance. The results suggest that executive and spatial components are important in the task, and raise questions about the role of preplanning in the TOL.     

The interaction between schizotypy and latent inhibition: modulation by experimental parameters

Two recent experiments (Della Casa et al., in press) yielded the typical reduced latent inhibition (LI) in high vs low schizotypy subjects after a slow, irregularly presented masking task (Stroop task), and reduced LI in low vs high schizotypy subjects after a fast, regularly presented masking task. The present experiment was aimed at testing whether speed or regularity was responsible for the different results. The present slow, regular experiment replicated the results of the former slow, irregular experiment, i.e. reduced LI in high schizotypals and significant LI in low schizotypals, indicating that speed and not regularity is the critical experimental variable. The modulation of the schizotypy—latent inhibition relationship can be attributed to differences in attentional resources or the time available to process the to-be-target stimuli during preexposure, in accordance with the hypothesis of Lubow and Gewirtz, 1995 that automatic processing of these stimuli is critical for the development of latent inhibition in adult humans. In addition, results on Stroop and negative priming effects are presented.     

Insights into spared memory capacity in amnestic MCI and Alzheimer's Disease via minimal interference

Impairment on standard tests of delayed recall is often already maximal in the aMCI stage of Alzheimer's Disease. Neuropathological work shows that the neural substrates of memory function continue to deteriorate throughout the progression of the disease, hinting that further changes in memory performance could be tracked by a more sensitive test of delayed recall. Recent work shows that retention in aMCI patients can be raised well above floor when the delay period is devoid of further material - 'Minimal Interference'. This memory enhancement is thought to be the result of improved memory consolidation. Here we used the minimal interference/interference paradigm (word list retention following 10 min of quiet resting vs. picture naming) in a group of 17 AD patients, 25 aMCI patients and 25 controls. We found (1) that retention can be improved significantly by minimal interference in patients with aMCI and patients with mild to moderate AD; (2) that the minimal interference paradigm is sensitive to decline in memory function with disease severity, even when performance on standard tests has reached floor; and (3) that this paradigm can differentiate well (80% sensitivity and 100% specificity) between aMCI patients who progress and do not progress to AD within 2 years. Our findings support the notion that the early memory dysfunction in AD is associated with an increased susceptibility to memory interference and are suggestive of a gradual decline in consolidation capacity with disease progression.     

Eye movements disrupt spatial but not visual mental imagery

It has long been known that eye movements are functionally involved in the generation and maintenance of mental images. Indeed, a number of studies demonstrated that voluntary eye movements interfere with mental imagery tasks (e.g., Laeng and Teodorescu in Cogn Sci 26:207–231, 2002). However, mental imagery is conceived as a multifarious cognitive function with at least two components, a spatial component and a visual component. The present study investigated the question of whether eye movements disrupt mental imagery in general or only its spatial component. We present data on healthy young adults, who performed visual and spatial imagery tasks concurrently with a smooth pursuit. In line with previous literature, results revealed that eye movements had a strong disruptive effect on spatial imagery. Moreover, we crucially demonstrated that eye movements had no disruptive effect when participants visualized the depictive aspects of an object. Therefore, we suggest that eye movements serve to a greater extent the spatial than the visual component of mental imagery.     

Context effects as auditory contrast

Three experiments are reported that collectively show that listeners perceive speech sounds as contrasting auditorily with neighboring sounds. Experiment 1 replicates the well-established finding that listeners categorize more of a [d–g] continuum as [g] after [l] than after [r]. Experiments 2 and 3 show that listeners discriminate stimuli in which the energy concentrations differ in frequency between the spectra of neighboring sounds better than those in which they do not differ. In Experiment 2, [alga–arda] pairs, in which the energy concentrations in the liquid-stop sequences are H(igh) L(ow)–LH, were more discriminable than [alda–arga] pairs, in which they are HH–LL. In Experiment 3, [da] and [ga] syllables were more easily discriminated when they were preceded by lower and higher pure tones, respectively—that is, tones that differed from the stops’ higher and lower F3 onset frequencies—than when they were preceded by H and L pure tones with similar frequencies. These discrimination results show that contrast with the target’s context exaggerates its perceived value when energy concentrations differ in frequency between the target’s spectrum and its context’s spectrum. Because contrast with its context does more that merely shift the criterion for categorizing the target, it cannot be produced by neural adaptation. The finding that nonspeech contexts exaggerate the perceived values of speech targets also rules out compensation for coarticulation by showing that their values depend on the proximal auditory qualities evoked by the stimuli’s acoustic properties, rather than the distal articulatory gestures.