Perceived Duration: The Interplay of Top-Down Attention and Task-Relevant Information.

Perception of time is susceptible to distortions; among other factors, it has been suggested that the perceived duration of a stimulus is affected by the observer's expectations. It has been hypothesized that the duration of an oddball stimulus is overestimated because it is unexpected, whereas repeated stimuli have a shorter perceived duration because they are expected. However, recent findings suggest instead that fulfilled expectations about a stimulus elicit an increase in perceived duration, and that the oddball effect occurs because the oddball is a target stimulus, not because it is unexpected. Therefore, it has been suggested that top-down attention is sometimes sufficient to explain this effect, and sometimes only necessary, with an additional contribution from saliency. However, how the expectedness of a target stimulus and its salient features affect its perceived duration is still an open question. In the present study, participants' expectations about and the saliency of target stimuli were orthogonally manipulated with stimuli presented on a short (Experiment 1) or long (Experiment 2) temporal scale. Four repetitive standard stimuli preceded each target stimulus in a task in which participants judged whether the target was longer or shorter in duration than the standards. Engagement of top-down attention to target stimuli increased their perceived duration to the same extent irrespective of their expectedness. A small but significant additional contribution to this effect from the saliency of target stimuli was dependent on the temporal scale of stimulus presentation. In Experiment 1, saliency only significantly increased perceived duration in the case of expected target stimuli. In contrast, in Experiment 2, saliency exerted a significant effect on the overestimation elicited by unexpected target stimuli, but the contribution of this variable was eliminated in the case of expected target stimuli. These findings point to top-down attention as the primary cognitive mechanism underlying the perceptual extraction and processing of task-relevant information, which may be strongly correlated with perceived duration. Furthermore, the scalar properties of timing were observed, favoring the pacemaker-accumulator model of timing as the underlying timing mechanism.

Transference effects of prior non-contingent reinforcement on the acquisition of temporal control on fixed-interval schedules.

In two experiments we examined the influence of response and time factors on the speed of acquisition of temporal control on FI schedules. In Experiment 1, prior exposure to FT accelerated the development of temporal control on FI schedules of the same temporal value. It was also found that the slower acquisition on FI with prior RT was similar to that of rats with prior standard training. In Experiment 2, prior exposure to FT accelerated the development of temporal control on a FI schedule with a threefold increase in temporal value. Additionally, it was found that with prior FI 30s training, acquisition of temporal control on FI 90s was even faster than with prior FT 30s. Measures of head-entries into the feeder along the experiments indicated that temporal control was already developed during the periodic but not during the non-periodic histories and that this control transferred to lever press during FI testing phase.

Effects of reinforcement history on response rate and response pattern in periodic reinforcement.

Several researchers have suggested that conditioning history may have long-term effects on fixed-interval performances of rats. To test this idea and to identify possible factors involved in temporal control development, groups of rats initially were exposed to different reinforcement schedules: continuous, fixed-time, and random-interval. Afterwards, half of the rats in each group were studied on a fixed-interval 30-s schedule of reinforcement and the other half on a fixed-interval 90-s schedule of reinforcement. No evidence of long-term effects attributable to conditioning history on either response output or response patterning was found; history effects were transitory. Different tendencies in trajectory across sessions were observed for measures of early and late responding within the interreinforcer interval, suggesting that temporal control is the result of two separate processes: one involved in response output and the other in time allocation of responding and not responding.

Ritmos de interacción social y ritmos biológicos: consistencia, sincronización y dependencia / Social interaction rhytms and biological rhytms: consistency synchronization and dependance

Se analizaron las actividades vocal y ventilatoria de pares de sujetos en situaciones de conversación. Los análisis de las series indicaron la presencia de componentes periódicos de ambas actividades, verificando la existencia de ritmos encontrados en otros estudios. Por lo general, los sujetos no fueron consistentes en los componentes rítmicos de actividad vocal y ventilatoria de una pareja a otra, aunque se observó cierta tendencia a mostrar sincronización se asoció con la familiaridad entre las parejas: las parejas con antecedentes de interacción no mostraron sincronización, mientras que las parejas sin antecedentes si tendieron a mostrar sincronización. Estos hallazgos se discuten en el contexto de proposiciones sobre la influencia de ritmos biológicos sobre los ritmos conductuales.

Vocal and ventilatory activity of dyads during conversation was analyzed. Analysis of the temporal series indicated the presence of periodic components in both activities, thus replicating what has been observed in other studies. In general, subjects did not show periodic components consisted across couples in either activity, but there was certain tendency to show synchronization in vocal activity. The later tendency was more clearly observed in couples whit antecedents of interaction that in those without it. Results are analyzed in the context of the proposal of the influence of biological rhythms on behavioral rhythms.