On additivity of duration reproduction functions

In the present paper properties of theoretical response functions in the duration reproduction task (drt) are studied. If the drt response is to be interpreted as the measure of a temporal duration elapsed in the past, the reproduction function (rf) must be additively measuring. The additivity property is defined for bivariate rfs, taking into account the delay between retention and reproduction. The requirement that an rf be additively measuring leads to a system of two functional equations, which are solved by (i) linear functions of time, or (ii) functions of the form yielded by the ‘dual klepsydra model’ of duration reproduction [Wackermann, J., & Ehm, W. (2006). The klepsydra model of internal time representation and time reproduction. Journal of Theoretical Biology, 239, 482-493]. This result supports the outstanding rôle of the ‘klepsydraic reproduction function’ (krf) in models of internal representation and reproduction of temporal durations.     

Is implicit sequence learning impaired in schizophrenia? A meta-analysis

Cognition in schizophrenia seems to be characterized by impaired performance on most tests of explicit or declarative learning contrasting with relatively intact performance on most tests of implicit or procedural learning. At the same time there have been conflicting results for studies that have used the Serial Reaction Time (SRT) task to examine implicit learning in people with schizophrenia. In the present research, we used meta-analysis to clarify whether or not people with schizophrenia show impaired performance on the SRT task. A systematic review found nine studies published in peer review journals that had each compared the performance of a group of people with schizophrenia with healthy controls on the standard SRT task or a variant of it. The resulting meta-analysis represented the responses of 205 participants with schizophrenia and 159 healthy controls on the SRT task. The analysis found that participants with schizophrenia perform less well than controls reflected by a pooled effect size of 0.51. A secondary analysis of all nine studies found that they all reported a point estimate of the change in reaction time between sequence and random trials that was greater for the controls. We conclude that there is a moderate impairment in implicit sequence learning among people with schizophrenia and speculate on the implications of this for understanding this disorder. Suggestions for improving the methodological quality and statistical reporting of studies of this topic are made.     

The hippocampus and prefrontal cortex are differentially involved in serial memory retrieval in non-stress and stress conditions

We previously showed that 24 h after learning, mice significantly remembered the first (D1) but not the second (D2) discrimination in a serial spatial task and that an acute stress delivered 5 min before the test phase reversed this memory retrieval pattern.A first experiment evaluated the effects of dorsal hippocampus (HPC) or prefrontal cortex (PFC) lesions, these two brain areas being well-known for their involvement in serial and spatial memory processes. For this purpose, six independent groups of mice were used: non-lesioned (controls), PFC or HPC-lesioned animals, submitted or not to an acute stress (electric footshocks; 0.9 mA). Results show that (i) non-stressed controls as well as PFC-lesioned mice (stressed or not) remembered D1 but not D2; (ii) stressed controls and HPC-lesioned mice (stressed or not) remembered D2 but not D1; (iii) stress significantly increased plasma corticosterone in controls and PFC-lesioned mice, but not in HPC-lesioned mice which already showed a significant plasma corticosterone increase in non-stressed condition.Since data from this first experiment showed that stress inhibited the hippocampal-dependent D1 memory retrieval, a second experiment evaluated the behavioral effect of intrahippocampal corticosterone injection in non-stressed mice. Results show that intrahippocampal corticosterone injection induced a reversal of serial memory retrieval pattern similar to that induced by acute stress.Overall, our study shows that (i) in non-stress condition, the emergence of D1 is HPC-dependent; (ii) in stress condition, the emergence of D2 requires the PFC integrity; moreover, intrahippocampal corticosterone injection mimicked the effects of stress in the CSD task.     

An analysis of immediate serial recall performance in a macaque

There has been considerable research into the ability of nonhuman primates to process sequential information, a topic that is of interest in part because of the extensive involvement of sequence processing in human language use. Surprisingly, no previous study has unambiguously tested the ability of nonhuman primates to encode and immediately reproduce a novel temporal sequence of perceptual events, the ability tapped in the immediate serial recall (ISR) task extensively studied in humans. We report here the performance of a rhesus macaque on a spatial ISR task, closely resembling tasks widely used in human memory research. Detailed analysis of the monkey’s recall performance indicates a number of important parallels with human ISR, consistent with the idea that a single mechanism for short-term serial order memory may be shared across species.     

Sticky plans: Inhibition and binding during serial-task control

Recent evidence suggests substantial response-time costs associated with lag-2 repetitions of tasks within explicitly controlled task sequences [Koch, I., Philipp, A. M., Gade, M. (2006). Chunking in task sequences modulates task inhibition. Psychological Science, 17, 346-350; Schneider, D. W. (2007). Task-set inhibition in chunked task sequences. Psychonomic Bulletin & Review, 14, 970-976], a result that has been interpreted as inhibition of no-longer relevant tasks. Experiments 1-3 confirm much larger lag-2 costs under serial-control than under externally cued conditions, but also show (a) that these costs occur only when sequences contain at least two distinct chunks and (b) that direct lag-2 repetitions are not a necessary condition for their occurrence. This pattern suggests the hypothesis that rather than task-set inhibition, the large lag-2 costs observed in complex sequences, reflect interference resulting from links between positions within a sequential plan and the individual tasks controlled by this plan. The remaining experiments successfully test this hypothesis (Experiment 4), rule out chaining accounts as a potential alternative explanation (Experiment 5), and demonstrate that interference results from information stored in long-term memory rather than working memory (Experiment 6). Implications of these results for an integration of models of serial-order control and serial memory are discussed.     

Monotonic weighted power transformations to additivity

A class of monotonic transformations which generalize the power transformation is fit to the independent and dependent variables in multiple regression so that the resulting additive relationship is optimized. This is achieved by minimizing a quadratic fitting criterion with linear inequality constraints on the parameters. A quadratic programming technique which works reliably and quickly in this application is outlined. Some examples of the analysis of artificial and real data are offered.This work was supported by National Research Council of Canada Grant APA 320 to the author.     

Fringe consciousness in sequence learning: the influence of individual differences

We first describe how the concept of “fringe consciousness” ([Mangan, 1993a], [Mangan, 1993b], [Mangan, 2001] and [Mangan, 2003]) can characterise gradations of consciousness between the extremes of implicit and explicit learning. We then show that the NEO-PI-R personality measure of openness to feelings, chosen to reflect the ability to introspect on fringe feelings, influences both learning and awareness in the serial reaction time (SRT) task under conditions that have previously been associated with implicit learning ([Destrebecqz and Cleeremans, 2001] and [Destrebecqz and Cleeremans, 2003]). This provides empirical evidence for the proposed phenomenology and functional role of fringe consciousness in so-called implicit learning paradigms (Mangan, 1993b). Introducing an individual difference variable also helped to identify possible limitations of the exclusion task as a measure of conscious sequence knowledge. Further exploration of individual differences in fringe awareness may help to avoid polarity in the implicit learning debate, and to resolve apparent inconsistencies between previous SRT studies.     

Bartlett revisited: Direct comparison of repeated reproduction and serial reproduction techniques

Bartlett developed the procedures of repeated reproduction (the same person repeatedly recalling information) and serial reproduction (people transmitting information from one person to another). Our experiment directly compared recall accuracy across these two techniques, which has not previously been reported, using DRM word lists. Recall of the initial study list words remained constant across repeated reproductions but declined markedly across serial reproductions. In contrast, recall of associated words that were not originally studied (i.e. critical words) was steady across both conditions. Because more of the original list words were forgotten across each link of the serial reproduction chain, the proportion of critical items recalled (relative to list words) increased significantly as the list passed between people. Using output bound scoring, serial reproduction resulted in lower accuracy than repeated reproduction by the final recall trial. Our results are broadly consistent with Bartlett's (1932) informal observations: Serial reproduction produces greater forgetting of the original material than does repeated reproduction and also leads to greater distortion relative to the proportion of correct material recalled.     

Single-probe serial position recall: Evidence of modularity for olfactory,visual, and auditory short-term memory

The present study examined and compared order memory for a list of sequentially presented odours, unfamiliar faces, and pure tones. Employing single-probe serial position recall and following a correction for a response bias, qualitatively different serial position functions were observed across stimuli. Participants demonstrated an ability to perform absolute order memory judgments for odours. Furthermore, odours produced an absence of serial position effects, unfamiliar faces produced both primacy and recency, and pure tones produced recency but not primacy. Such a finding is contrary to the proposal by Ward, Avons, and Melling (2005) that the serial position function is task, rather than modality, dependent. In contrast, the observed functions support a modular conceptualization of short-term memory (e.g., Andrade & Donaldson, 2007; Baddeley & Hitch, 1974), whereby separate modality-specific memorial systems operate. An alternative amodal interpretation is also discussed wherein serial position function disparities are accommodated via differences in the psychological distinctiveness of stimuli (Hay, Smyth, Hitch, & Horton, 2007).