Variable Foreperiods and Temporal Discrimination

Temporal judgements are often accounted for by a single-clock hypothesis. The output of such a clock is reported to depend on the allocation of attention. In the present series of experiments, the influence of attention on temporal information processing is investigated by systematic variations of the period preceding brief empty intervals to be judged. Two indicators of timing performance, temporal sensitivity, reflecting discrimination performance, and perceived duration served as dependent variables. Foreperiods ranged from 0.3 to 0.6 s in Experiments 1 to 4. When the foreperiod varied randomly from trial to trial, perceived duration was longer with increasing length of foreperiod (Experiments 1 and 3 with brief auditory markers and Experiment 4 with brief visual markers), an effect that disappeared with no trial-to-trial variations (Experiment 2). Longer foreperiods also enhanced performance on temporal discrimination of auditory empty intervals with a base duration of 100 ms (Experiments 1 and 5), whereas discrimination performance was unaffected for auditory intervals with a base duration of 500 ms (Experiment 3). The variable-foreperiod effect on perceived duration also held when foreperiods ranged from 0.6 to 1.5 s (Experiments 5—7). Findings suggest that foreperiods appear to effectively modulate attention mechanisms necessary for temporal information processing. However, alternative explanations such as assimilation or compatibility effects cannot be totally discarded.

DESCRIPTION OF THE PREPARATORY STAGES OF NEONYMPHA AREOLATUS, Smith–Abbot

Egg—Nearly globular; the surface smooth under a low power, but under a high one, thickly covered with shallow depressions, which are irregular in size and also in form, being pentagonal, rounded or oval; color pale green. Duration of this stage about 6 days.Young Larva.—Length .12 inch; cylindrical, nearly even, tapering a little posteriorly, the last segment bluntly forked; color delicate green; over the surface many white hairs, and among these are black clubbed hairs disposed in longitudinal rows, four on the dorsum of each segment, two in front, two in rear; feet and legs green; head large, about twice as broad as any body segment, sub-globose, a little depressed at top; on each vertex a short semi-ovoid appendage, at the top giving out two divergent black hairs; just below vertex, on the front, is a similar smaller appendage with single hair, and on the side half way down is a second; color black. Towards the end of this stage the color of body changes to decided green, and several longitudinal stripes appear; on either side of a dark green medio-dorsal stripe is a whitish one, a similar one on middle of side and another along base. Duration of this stage about 8 days, but depending on the weather.