A challenge for researchers in the time-perception field is to determine whether temporal processing is governed by a central mechanism or by multiple mechanisms working in concert. Behavioral studies of parallel timing offer interesting insights into the question, although the conclusions fail to converge. Most of these studies focus on the number-of-clocks issue, but the commonality of memory mechanisms involved in time processing is often neglected. The present experiment aims to address a straightforward question: do signals from different modalities marking time intervals share the same clock and/or the same memory resources? To this end, an interval reproduction task involving the parallel timing of two sensory signals presented either in the same modality or in different modalities was conducted. The memory component was tested by manipulating the delay separating the presentation of the target intervals and the moment when the reproduction of one of these began. Results show that there is more variance when only visually marked intervals are presented, and this effect is exacerbated with longer retention delays. Finally, when there is only one interval to process, encoding the interval with signals delivered from two modalities helps to reduce variance. Taken together, these results suggest that the hypothesis stating that there are sensory-specific clock components and memory mechanisms is viable.

We investigated how does the structure of empty time intervals influence temporal processing. In experiment 1, the intervals to be discriminated were the silent durations marked by two sensory signals, both lasting 10 or 500 ms; these signals were two identical flashes (intramodal: VV), or one visual flash (V) followed by an auditory tone (A) (intermodal: VA). For the range of duration under investigation (standards = 0.2, 0.6, 1, or 1.4 s), the results indicated that both the marker length and sensory mode influenced discrimination, but no interaction between these variables or between one of these variables and standard duration was significant. In experiment 2, we compared, for each of four marker-type conditions (VV, AA, VA, AV; and standard = 1 s), intervals marked by two 10 ms signals with intervals marked by unequal signal length (markers 1 and 2 lasting 10 and 500 ms, or 500 and 10 ms). As in experiment 1, the results revealed significant marker-mode and marker-length effects, but no significant interaction between these variables. Experiment 3 showed that, for the same conditions as in experiment 2, perceived duration is not influenced by marker length and that the variability of interval reproductions does not depend on the perceived duration of intervals. The results are discussed in the light of a single-clock hypothesis: marker-length and marker-mode effects are presented as being non-temporal sources of variability associated mainly with sensory and memory processes.

To further explore how memory influences time judgments, we conducted two experiments on the lifespan of temporal representations in memory. Penney et al (2000, Journal of Experimental Psychology Human Perception and Performance 26 1770-1787) reported that the perceived duration of auditorily and visually marked intervals differs only when both marker-type intervals are compared directly. This finding can be explained by a 'memory-mixing' process, whereby the memory trace of previous intervals influences the perception of upcoming ones, which are then added to the memory content. In the experiments discussed here, we manipulated the mixing mode of auditory/visual signal presentations. In experiment 1, signals from the same modality were either grouped by blocks or randomised within blocks. The results showed that the auditory/visual difference decreased but remained present when modalities were grouped by blocks. In experiment 2, we used a line-segmentation task. The results showed that, after a training block was performed in one modality, the perceived duration of signals from the other modality was distorted for at least 30 trials and that the magnitude of the difference decreased as the block went on. The results of both experiments highlight the influence of memory on time judgments, providing empirical support to, and quantitative portrayal of, the memory-mixing process.

ABSTRACT:Background:The age-at-onset (AAO) of Parkinson’s disease (PD) is thought to be influenced by environmental factors and polygenic predispositions. Professional exposures to pesticides and toxic metals were shown to be associated with an earlier onset in small sample studies.Aim of Study:The aim of this study was to confirm the association between professional exposures to pesticides and toxic metals and the AAO of PD, on a larger cohort of patients, defined with a clinic-based ascertainment scheme.Methods:We used an incident cohort of 290 patients recruited through three designated movement disorder clinics in the province of Quebec, Canada. Patients completed a detailed questionnaire regarding professional exposures to pesticides and toxic metals. We compared the AAO in patients without prior professional exposure (N = 170) and those with exposure to pesticides (N = 53) or toxic metals through welding (N = 30). We further subdivided patients exposed to pesticides according to the frequency and proximity of their contacts.Results:Patients with prior exposure to pesticides (AAO = 54.74 years) or toxic metals (54.27 years) had a significantly earlier AAO compared to the control group (59.26 years) (p = 0.003). In those exposed to pesticides, closer (p = 0.03) and more frequent (p = 0.02) contacts were negatively correlated with AAO.Conclusion:Exposure to pesticides and toxic metals were both associated with an earlier onset of PD, an effect that was greater with higher levels of exposure, both in terms of frequency and proximity.

The learning principles underlying well conducted simulator-based education programmes have a strong scientific basis. A simulator training programme like this one represents a promising avenue for driving rehabilitation. It allows individuals without a driving license to practice and improve their skills in a safe and realistic environment.