Attention and time estimation in 5- and 8-year-old children: a dual-task procedure

This experiment tested the effect of a dual-task on time reproduction in 5- and 8-year-olds. Children had to reproduce a stimulus duration lasting for 6 or 12 s, during which they either did or did not perform a concurrent non-temporal task (i.e. picture naming) both in low (LA) and high (HA) attentional demand conditions. The results showed that children reproduced shorter durations in the dual-task than in the single-task condition, whatever the duration value used. However, this shortening effect was greater in the 5-year-olds than in the 8-year-olds. Furthermore, in the 5-year-olds, temporal reproductions were significantly shorter in both dual-tasks (LA or HA) than in the single-task, whereas, in the 8-year-olds, differences reached significance only between the HA dual-task and the single-task. In the non-temporal task, the proportion of naming errors was also greater in the dual-task than in the single-task, especially under high attentional demand, but it did not significantly differ between the two age groups tested.     

Group Choice as a Function of Group Size Differences and Assessment Time in Fish: The Influence of Species Vulnerability to Predation

The shoal-choice behaviour of two species of fish that differ in their vulnerability to predation was compared. Individuals of threespine stickleback, Gasterosteus aculeatus, and creek chub, Semotilus atromaculatus, were presented with a simultaneous choice of two equidistant stimulus shoals of conspecifics that differed in membership size (5 vs. 6 fish, 5 vs. 7, 5 vs. 8, 5 vs. 9 and 5 vs. 10). Test fish were allowed to view the stimulus shoals from a standard distance for either 10–20 or 120–150s before being frightened with a stimulus from an overhead light and released to join either shoal. We observed which shoal (the smaller or the larger one) the test fish approached. Preference for the larger stimulus shoal generally increased with increasing shoal size difference and with the duration of the assessment period, and was more pronounced in chub (the more vulnerable of the two species). For the short assessment period, chub showed a significantly stronger preference for the larger stimulus shoal than sticklebacks, whereas there was no significant difference between species for the long assessment period. Furthermore, chub responded more readily to small differences in shoal size (of 1–3 fish) than sticklebacks, for both short and long assessment periods. The above results are consistent with the hypothesis that chub, as the more vulnerable of the two species (in terms of predation), should be able to identify the larger of two shoals more quickly and should be more sensitive to small differences in shoal size than sticklebacks.     

Counting in a time discrimination task in children and adults

The present study investigated in 5- and 8-year-olds, as well as in adults, the effect of verbal counting on temporal discrimination behavior in a generalization task with two duration ranges in order to test the scalar timing property. The results showed that counting improved temporal sensitivity in all age groups, although sensitivity to time remained lower in the younger children. Furthermore, in the 5-year-olds, the temporal generalization behavior conformed well to the scalar property of variance both in the counting and the non-counting condition. However, this conformity to the scalar timing property disappeared when counting was used in the 8-year-olds and the adults. The development of the ability to count time at a constant rhythm is discussed as the major reason for this departure of temporal behavior from the scalar property of variance when counting is employed.     

The failure of Weber's law in time perception and production

Weber's law--constancy of the coefficient of variation--is an apparently ubiquitous feature of time perception, and forms the foundation of several theories of timing. We sought evidence for Weber's law in temporal production and categorization experiments. The production task required pigeons to switch between keys within a specified temporal window. The categorization task required them to classify a stimulus duration as either short or long. Weber fractions did not descend to a horizontal asymptote, but were U-shaped: they decreased as a function of target duration, and increased again at intermediate and long durations. This pattern conforms neither to Weber's law, nor to its generalized form (Getty, D.J., 1975. Discrimination of short temporal intervals: a comparison of two models. Percept. Psychophys. 18, 1-8). A model of counter failure accommodated the U-shaped pattern.     

No childhood advantage in the acquisition of skill in using an artificial language rule

A leading notion is that language skill acquisition declines between childhood and adulthood. While several lines of evidence indicate that declarative ("what", explicit) memory undergoes maturation, it is commonly assumed that procedural ("how-to", implicit) memory, in children, is well established. The language superiority of children has been ascribed to the childhood reliance on implicit learning. Here we show that when 8-year-olds, 12-year-olds and young adults were provided with an equivalent multi-session training experience in producing and judging an artificial morphological rule (AMR), adults were superior to children of both age groups and the 8-year-olds were the poorest learners in all task parameters including in those that were clearly implicit. The AMR consisted of phonological transformations of verbs expressing a semantic distinction: whether the preceding noun was animate or inanimate. No explicit instruction of the AMR was provided. The 8-year-olds, unlike most adults and 12-year-olds, failed to explicitly uncover the semantic aspect of the AMR and subsequently to generalize it accurately to novel items. However, all participants learned to apply the AMR to repeated items and to generalize its phonological patterns to novel items, attaining accurate and fluent production, and exhibiting key characteristics of procedural memory. Nevertheless, adults showed a clear advantage in learning implicit task aspects, and in their long-term retention. Thus, our findings support the notion of age-dependent maturation in the establishment of declarative but also of procedural memory in a complex language task. In line with recent reports of no childhood advantage in non-linguistic skill learning, we propose that under some learning conditions adults can effectively express their language skill acquisition potential. Altogether, the maturational effects in the acquisition of an implicit AMR do not support a simple notion of a language skill learning advantage in children.     

Reduced susceptibility to interference in the consolidation of motor memory before adolescence

Are children superior to adults in consolidating procedural memory? This notion has been tied to "critical," early life periods of increased brain plasticity. Here, using a motor sequence learning task, we show, in experiment 1, that a) the rate of learning during a training session, b) the gains accrued, without additional practice, within a 24 hours post-training interval (delayed consolidation gains), and c) the long-term retention of these gains, were as effective in 9, 12 and 17-year-olds and comparable to those reported for adults. However, a follow-up experiment showed that the establishment of a memory trace for the trained sequence of movements was significantly more susceptible to interference by a subsequent motor learning experience (practicing a reversed movement sequence) in the 17-year-olds compared to the 9 and 12-year-olds. Unlike the 17-year-olds, the younger age-groups showed significant delayed gains even after interference training. Altogether, our results indicate the existence of an effective consolidation phase in motor learning both before and after adolescence, with no childhood advantage in the learning or retention of a motor skill. However, the ability to co-consolidate different, successive motor experiences, demonstrated in both the 9 and 12-year-olds, diminishes after puberty, suggesting that a more selective memory consolidation process takes over from the childhood one. Only the adult consolidation process is gated by a recency effect, and in situations of multiple, clashing, experiences occurring within a short time-interval, adults may less effectively establish in memory experiences superseded by newer ones.     

Time changes with the embodiment of another's body posture

The aim of the present study was to investigate whether the perception of presentation durations of pictures of different body postures was distorted as function of the embodied movement that originally produced these postures. Participants were presented with two pictures, one with a low-arousal body posture judged to require no movement and the other with a high-arousal body posture judged to require considerable movement. In a temporal bisection task with two ranges of standard durations (0.4/1.6 s and 2/8 s), the participants had to judge whether the presentation duration of each of the pictures was more similar to the short or to the long standard duration. The results showed that the duration was judged longer for the posture requiring more movement than for the posture requiring less movement. However the magnitude of this overestimation was relatively greater for the range of short durations than for that of longer durations. Further analyses suggest that this lengthening effect was mediated by an arousal effect of limited duration on the speed of the internal clock system.     

The Effect of Stimulus Duration on Frequency-Response Functions in the Pacinian (P) Channel

Psychophysical experiments on human observers and physiological measurements on Pacinian corpuscles (PCs) isolated from cat mesentery were performed to explain certain discrepancies in the psychophysical—physiological model (Bolanowski et al., 1988) for the sense of touch in the vibrotactle Pacinian (P) channel. The model was based on correlations among the psychophysical frequency response obtained on human glabrous skin and physiological frequency-response functions measured on two PC preparations: PC fibers innervating human glabrous skin (Johansson et al., 1982) and PCs isolated from cat mesentery. The three frequency-response functions were qualitatively similar. However, the low-frequency slope for the human PC fibers differed from the slopes for the psychophysical and cat mesentery PC functions by being 3 dB/octave less steep. This discrepancy can be explained theoretically by differences in methodology involving the effect of stimulus duration and the property of temporal summation known to exist in the P channel (i.e., a 3-dB increase in sensitivity per doubling of stimulus duration). To test this, experiments were performed using two methods of stimulation: (1) a constant stimulus duration for different test frequencies, as generally used in this laboratory; and (2) a constant number of stimulus cycles (n = 5) for each test frequency as used by Johansson et al. The method of least squares was used to calculate the low-frequency (50 to 150-Hz) slopes of individual psychophysical and physiological functions. The mean slopes that resulted from using the two methods of stimulation were consistent with the theoretical expectations.     

Reduced variability of ongoing and evoked cortical activity leads to improved behavioral performance

Sensory responses of the brain are known to be highly variable, but the origin and functional relevance of this variability have long remained enigmatic. Using the variable foreperiod of a visual discrimination task to assess variability in the primate cerebral cortex, we report that visual evoked response variability is not only tied to variability in ongoing cortical activity, but also predicts mean response time. We used cortical local field potentials, simultaneously recorded from widespread cortical areas, to gauge both ongoing and visually evoked activity. Trial-to-trial variability of sensory evoked responses was strongly modulated by foreperiod duration and correlated both with the cortical variability before stimulus onset as well as with response times. In a separate set of experiments we probed the relation between small saccadic eye movements, foreperiod duration and manual response times. The rate of eye movements was modulated by foreperiod duration and eye position variability was positively correlated with response times. Our results indicate that when the time of a sensory stimulus is predictable, reduction in cortical variability before the stimulus can improve normal behavioral function that depends on the stimulus.     

Exploring the cortical evidence of a sensory-discrimination process

Humans and monkeys have similar abilities to discriminate the difference in frequency between two consecutive mechanical vibrations applied to their fingertips. This task can be conceived as a chain of neural operations: encoding the two consecutive stimuli, maintaining the first stimulus in working memory, comparing the second stimulus with the memory trace left by the first stimulus and communicating the result of the comparison to the motor apparatus. We studied this chain of neural operations by recording and manipulating neurons from different areas of the cerebral cortex while monkeys performed the task. The results indicate that neurons of the primary somatosensory cortex (S1) generate a neural representation of vibrotactile stimuli which correlates closely with psychophysical performance. Discrimination based on microstimulation patterns injected into clusters of S1 neurons is indistinguishable from that produced by natural stimuli. Neurons from the secondary somatosensory cortex (S2), prefrontal cortex and medial premotor cortex (MPC) display at different times the trace of the first stimulus during the working-memory component of the task. Neurons from S2 and MPC appear to show the comparison between the two stimuli and correlate with the behavioural decisions. These neural operations may contribute to the sensory-discrimination process studied here.     

Auditory event-related potentials dissociate early and late memory processes

Event-related potentials (ERPs) to environmental sounds were recorded from 15 young control subjects in an auditory recognition memory task. Subjects listened to a continuous string of binaurally presented sounds, 20% of which were presented once and 80% were repeated. Of the repeated sounds, some repeated immediately after the initial presentation (2 sec; short delay repetition) while others repeated after 2–6 intervening sounds (4–12 sec; long delay repetition). Subjects were instructed to indicate whether they had heard the sounds before by pressing a “yes” or “no” button.The initial stimulus presentation and long delay repetition stimuli generated both an N4 component and a prolonged latency P3 component while the short delay repetition stimuli elicited no N4 component and an earlier latency P3 component. Subjects' responses were faster and more accurate for short delay repetition. All stimuli generated a sustained frontal negative component (SFN). These data indicate that auditory recognition memory for environmental sounds may involve two processes. The P3 generated by both short and long delay repetition stimuli may index activation of a neocortical template matching system. The N4 generated by initial stimulus presentations and long delay repetition is proposed to measure additional activation of limbic memory systems at long retention intervals.     

Rapid-Eye-Movement-Sleep (REM) Associated Enhancement of Working Memory Performance after a Daytime Nap

The main objective was to study the impact of a daytime sleep opportunity on working memory and the mechanism behind such impact. This study adopted an experimental design in a sleep research laboratory. Eighty healthy college students (Age:17-23, 36 males) were randomized to either have a polysomnography-monitored daytime sleep opportunity (Nap-group, n=40) or stay awake (Wake-group, n=40) between the two assessment sessions. All participants completed a sleep diary and wore an actigraph-watch for 5 days before and one day after the assessment sessions. They completed the state-measurement of sleepiness and affect, in addition to a psychomotor vigilance test and a working memory task before and after the nap/wake sessions. The two groups did not differ in their sleep characteristics prior to and after the lab visit. The Nap-group had higher accuracy on the working memory task, fewer lapses on the psychomotor vigilance test and lower state-sleepiness than the Wake-group. Within the Nap-group, working memory accuracy was positively correlated with duration of rapid eye movement sleep (REM) and total sleep time during the nap. Our findings suggested that “sleep gain” during a daytime sleep opportunity had significant positive impact on working memory performance, without affecting subsequent nighttime sleep in young adult, and such impact was associated with the duration of REM. While REM abnormality has long been noted in pathological conditions (e.g. depression), which are also presented with cognitive dysfunctions (e.g. working memory deficits), this was the first evidence showing working memory enhancement associated with REM in daytime napping in college students, who likely had habitual short sleep duration but were otherwise generally healthy.     

Comparisons of an Open-Ended vs. Forced-Choice ‘Mind Reading’ Task: Implications for Measuring Perspective-Taking and Emotion Recognition

Perspective-taking and emotion recognition are essential for successful social development and have been the focus of developmental research for many years. Although the two abilities often overlap, they are distinct and our understanding of these abilities critically rests upon the efficacy of existing measures. Lessons from the literature differentiating recall versus recognition memory tasks led us to hypothesize that an open-ended emotion recognition measure would be less reliant on compensatory strategies and hence a more specific measure of emotion recognition abilities than a forced-choice task. To this end, we compared an open-ended version of the Reading the Mind in the Eyes Task with the original forced-choice version in two studies: 118 typically-developing 4- to 8-year-olds (Study 1) and 139 5- to 12-year-olds; 85 typically-developing and 54 with learning disorders (Study 2). We found that the open-ended version of the task was a better predictor of empathy and more reliably discriminated typically-developing children from those with learning disorders. As a whole, the results suggest that the open-ended version is a more sensitive measure of emotion recognition specifically.     

IL-2 secretion by CD4+ T cells in vivo is rapid, transient, and influenced by TCR-specific competition

The secretion of IL-2 is a critical and early landmark in the activation program of CD4(+) T cells in vitro, but the lack of sensitive assays has limited its application for studying T cell activation in vivo. Using a mouse cytokine capture assay we were able to detect the rapid secretion of IL-2 after an in vivo stimulus by 1-2 h in naive T cells and as early as 30 min in memory T cells. Maximal secretion was achieved within 1-2 h for memory cells or 6-8 h for naive T cells. Surprisingly IL-2 production terminated quickly in vivo and secretion was undetectable by 20-24 h in either cell type. We further demonstrated that this short duration of secretion can be influenced by cellular competition between Ag-specific CD4(+) T cells. The consequences of competition were mimicked by reducing the strength of the antigenic stimulus. These data argue that early competition between T cells influences both the eventual frequency of IL-2 producers in the population and also the duration of their secretion, potentially by altering the strength or duration of the stimulus available to each T cell.     

Determinants of excitability in cardiac myocytes: mechanistic investigation of memory effect

The excitability of a cardiac cell depends upon many factors, including the rate and duration of pacing. Furthermore, cell excitability and its variability underlie many electrophysiological phenomena in the heart. In this study, we used a detailed mathematical model of the ventricular myocyte to investigate the determinants of excitability and gain insight into the mechanism by which excitability depends on the rate and duration of pacing (the memory effect). Results: i) The primary determinant of excitability depends upon the duration (T) of the stimulus. ii) For a short T, excitability is determined by the difference between the threshold membrane potential and the resting membrane potential. iii) For a long T, excitability is determined by the resting membrane resistance, R(m). iv) In the case of long T, pacing induced changes in [Na(+)](i) and [Ca(2+)](i) over time affect R(m) and excitability by shifting the current-voltage (IV) curve in the vertical direction and are responsible for the memory effect. CONCLUSIONS: The results have important implications during an arrhythmia, where a cardiac cell may be subjected to rapid repetitive excitation for an extended period of time. Effective anti-arrhythmic strategies may be developed to exploit the R(m) dependence of excitability for a long T.     

Implicit, predictive timing draws upon the same scalar representation of time as explicit timing

It is not yet known whether the scalar properties of explicit timing are also displayed by more implicit, predictive forms of timing. We investigated whether performance in both explicit and predictive timing tasks conformed to the two psychophysical properties of scalar timing: the Psychophysical law and Weber's law. Our explicit temporal generalization task required overt estimation of the duration of an empty interval bounded by visual markers, whereas our temporal expectancy task presented visual stimuli at temporally predictable intervals, which facilitated motor preparation thus speeding target detection. The Psychophysical Law and Weber's Law were modeled, respectively, by (1) the functional dependence between mean subjective time and real time (2) the linearity of the relationship between timing variability and duration. Results showed that performance for predictive, as well as explicit, timing conformed to both psychophysical properties of interval timing. Both tasks showed the same linear relationship between subjective and real time, demonstrating that the same representational mechanism is engaged whether it is transferred into an overt estimate of duration or used to optimise sensorimotor behavior. Moreover, variability increased with increasing duration during both tasks, consistent with a scalar representation of time in both predictive and explicit timing. However, timing variability was greater during predictive timing, at least for durations greater than 200 msec, and ascribable to temporal, rather than non-temporal, mechanisms engaged by the task. These results suggest that although the same internal representation of time was used in both tasks, its external manifestation varied as a function of temporal task goals.     

Dopamine agonists and antagonists can produce an attenuation of response bias in a temporal discrimination task depending on discriminability of target duration

The current study examined the effects of the D2 agonist (quinpirole) and D2 antagonist (eticlopride) on temporal discrimination performance in a conditional discrimination task (Experiment I) and a delayed conditional discrimination task (Experiment II). In both experiments rats discriminated between a scheduled stimulus duration of 3 s versus 9 s. Consistent with previous reports, overall discrimination performance decreased in a dose-dependent manner with both drugs. Changes in response bias (the tendency to choose-short or choose-long irrespective of actual stimulus duration), however, were best characterized in terms of both drugs tending to attenuate the bias effects normally observed during baseline drug-free performance. Specifically, the 'choose-short' bias observed in Experiment I and at a relatively short, 0.1 s, delay in Experiment II became less extreme with increasing doses. In addition, the 'choose-long' bias observed at a relatively long, 6 s, delay in Experiment II also became less extreme with increasing doses. Thus, whether there was an apparent shift from a short response bias to long, or vice versa, was the product of the delay interval between stimulus presentation and choice rather than whether the drug in question was a D2 agonist or antagonist. Such an attenuation of bias may have arisen because of subjects confounding the delay interval with the actual discriminative stimulus duration.     

Testicular development in Siberian hamsters depends on frequency and pattern of melatonin signals

We investigated the impact of frequency and pattern of melatonin signals on reproductive development in Siberian hamsters. Juvenile males gestated in short day lengths and housed in constant illumination to suppress melatonin secretion were infused with melatonin for 5 h either once or twice per day for 20 days. Melatonin infusions at either frequency produced equivalent increases in testes and body weights that exceeded those of animals infused with saline but were indistinguishable from those of hamsters transferred to long day lengths. The reproductive system appears to be maximally stimulated by a single short melatonin signal each day. Other animals kept from birth in a short photoperiod were treated 6 h after onset of darkness with the beta-adrenergic receptor antagonist DL-propranolol to shorten melatonin secretion on the night of injection but not on subsequent nights. This permitted interpolation of short nightly melatonin signals of 4-5 h duration against a background of long melatonin signals of 10-12 h duration on other nights. Treatment regimes that maintained a 1:1 ratio of short to long melatonin signals for 8 wk stimulated reproductive development; a 1:2 signal ratio, in each of three different patterns, was uniformly ineffective. The number of successive short melatonin signals had little influence on the interval across which successive melatonin signals were summated to influence photoperiodic traits. The neuroendocrine axis appears more responsive to short melatonin signal frequency than pattern for development of the summer phenotype.     

The effect of study-test modalities on the remembrance of subjective duration from long-term memory

It was examined whether stimulus modality (auditory vs. visual) affects the retrieval of subjective duration from memory. In two experiments the temporal generalization paradigm was used. Participants had to decide whether the previously learned standard duration (400 ms) occurred in the context of comparison stimuli. Two major results were found. (1) Discrimination was more accurate if the training and testing stimuli were of the same modality than if they were of opposite modalities. (2) If both modality of learning and modality of testing were different, subjects systematically underestimated the test durations, i.e. temporal generalization gradients (the proportion of identifications of a stimulus as the standard, plotted against stimulus duration) shifted to the right. The observed shift is interpreted as a result of a delayed timing process.     

Diminished Activation of Motor Working-Memory Networks in Parkinson's Disease

Parkinson''s disease (PD) is characterized by typical extrapyramidal motor features and increasingly recognized non-motor symptoms such as working memory (WM) deficits. Using functional magnetic resonance imaging (fMRI), we investigated differences in neuronal activation during a motor WM task in 23 non-demented PD patients and 23 age- and gender-matched healthy controls. Participants had to memorize and retype variably long visuo-spatial stimulus sequences after short or long delays (immediate or delayed serial recall). PD patients showed deficient WM performance compared to controls, which was accompanied by reduced encoding-related activation in WM-related regions. Mirroring slower motor initiation and execution, reduced activation in motor structures such as the basal ganglia and superior parietal cortex was detected for both immediate and delayed recall. Increased activation in limbic, parietal and cerebellar regions was found during delayed recall only. Increased load-related activation for delayed recall was found in the posterior midline and the cerebellum. Overall, our results demonstrate that impairment of WM in PD is primarily associated with a widespread reduction of task-relevant activation, whereas additional parietal, limbic and cerebellar regions become more activated relative to matched controls. While the reduced WM-related activity mirrors the deficient WM performance, the additional recruitment may point to either dysfunctional compensatory strategies or detrimental crosstalk from “default-mode” regions, contributing to the observed impairment.