Modality and intermittency effects on time estimation

The modality of a stimulus and its intermittency affect time estimation. The present experiment explores the effect of a combination of modality and intermittency, and its implications for internal clock explanations. Twenty-four participants were tested on a temporal bisection task with durations of 200-800 ms. Durations were signaled by visual steady stimuli, auditory steady stimuli, visual flickering stimuli, and auditory clicks. Psychophysical functions and bisection points indicated that the durations of visual steady stimuli were classified as shorter and more variable than the durations signaled by the auditory stimuli (steady and clicks), and that the durations of the visual flickering stimuli were classified as longer than the durations signaled by the auditory stimuli (steady and clicks). An interpretation of the results is that there are different speeds for the internal clock, which are mediated by the perceptual features of the stimuli timed, such as differences in time of processing.     

Time estimation of fear cues in human observers

Previous research suggests that time judgments are a function of the affective properties of to-be-timed stimuli and that time judgments are longer for stimuli that are fear-inducing (e.g., [Hare, 1963] and [Watts and Sharrock, 1984]). The goals of the present study were twofold: to replicate the effect of a fear cue on time estimation, and to evaluate the mechanism underlying the effect. Seven stimulus durations in two different duration ranges (short: 250-1000 ms; long: 400-1600 ms) were employed in the bisection procedure. Adult human participants were exposed to two successive sessions, one each with the short and long range. Images from the International Affective Picture System (IAPS; Lang et al., 2008) that were rated on three scales including arousal and fear were presented as temporal stimuli. Three images that were rated high on fear and three rated low served as fear cues and neutral control images, respectively. Results indicated that for both ranges, judgments were longer for fear cues than for neutral images, and that the magnitude of the effect did not differ between ranges as measured by the bisection point. Application of scalar expectancy theory (SET; [Gibbon, 1977] and [Church, 1984]) to these results suggests that the fear effects were mediated by switch latency of an internal clock, rather than by clock speed.     

Temporal acuity of honeybee vision: behavioural studies using flickering stimuli

ABSTRACT. Temporal resolution of freely-flying bees was measured by training bees, Apis mellifera (Linn.), to discriminate between a steady light and a flickering light. Two kinds of experiments were conducted: those using a homochromatic flicker, in which the intensity of the flickering light varied periodically with time; and ones using a heterochromatic flicker, in which the colour of the flickering light varied periodically. In either case, the time-averaged properties (intensity and colour) of the flickering light matched those of the steady light, and the bees' ability to discriminate between the two stimuli was measured for various flicker frequencies. The results indicate that bees perform poorly in the homochromatic flicker experiments, regardless of the colour of the light (u.v., blue or green), but well in those with heterochromatic flicker. Heterochromatic flicker experiments using various pairwise combinations of the colours U.V., blue and green (corresponding to the three known spectral receptor-types in the bee's retina) reveal that temporal resolution is much better when blue is one of the component colours, than when it is not. The simplest interpretation of the results is in terms of colour channels possessing different response speeds. Heterochromatic flicker promises to be a useful tool in investigating the temporal properties of colour vision in bees.     

How Long Depends on How Fast—Perceived Flicker Dilates Subjective Duration

How do humans perceive the passage of time and the duration of events without a dedicated sensory system for timing? Previous studies have demonstrated that when a stimulus changes over time, its duration is subjectively dilated, indicating that duration judgments are based on the number of changes within an interval. In this study, we tested predictions derived from three different accounts describing the relation between a changing stimulus and its subjective duration as either based on (1) the objective rate of changes of the stimulus, (2) the perceived saliency of the changes, or (3) the neural energy expended in processing the stimulus. We used visual stimuli flickering at different frequencies (4–166 Hz) to study how the number of changes affects subjective duration. To this end, we assessed the subjective duration of these stimuli and measured participants'' behavioral flicker fusion threshold (the highest frequency perceived as flicker), as well as their threshold for a frequency-specific neural response to the flicker using EEG. We found that only consciously perceived flicker dilated perceived duration, such that a 2 s long stimulus flickering at 4 Hz was perceived as lasting as long as a 2.7 s steady stimulus. This effect was most pronounced at the slowest flicker frequencies, at which participants reported the most consistent flicker perception. Flicker frequencies higher than the flicker fusion threshold did not affect perceived duration at all, even if they evoked a significant frequency-specific neural response. In sum, our findings indicate that time perception in the peri-second range is driven by the subjective saliency of the stimulus'' temporal features rather than the objective rate of stimulus changes or the neural response to the changes.     

Conscious awareness of flicker in humans involves frontal and parietal cortex

Even when confined to the same spatial location, flickering and steady light evoke very different conscious experiences because of their distinct temporal patterns. The neural basis of such differences in subjective experience remains uncertain . Here, we used functional MRI in humans to examine the neural structures involved in awareness of flicker. Participants viewed a single point source of light that flickered at the critical flicker fusion (CFF) threshold, where the same stimulus is sometimes perceived as flickering and sometimes as steady (fused) . We were thus able to compare brain activity for conscious percepts that differed qualitatively (flickering or fused) but were evoked by identical physical stimuli. Greater brain activation was observed on flicker (versus fused) trials in regions of frontal and parietal cortex previously associated with visual awareness in tasks that did not require detection of temporal patterns . In contrast, greater activation was observed on fused (versus flicker) trials in occipital extrastriate cortex. Our findings indicate that activity of higher-level cortical areas is important for awareness of temporally distinct visual events in the context of a nonspatial task, and they thus suggest that frontal and parietal regions may play a general role in visual awareness.     

Time perception,depression and sadness

This study examined changes in time perception as a function of depressive symptoms, assessed for each participant with the Beck Depression Inventory (BDI). The participants performed a temporal bisection task in which they had to categorize a signal duration of between 400 and 1600 ms as either as short or long. The data showed that the bisection function was shifted toward the right, and that the point of subjective equality was higher in the depressive than in the non-depressive participants. Furthermore, the higher the depression score was, the shorter the signal duration was judged to be. In contrast, the sensitivity to time was similar in these two groups of participants. These results thus indicate that the probe durations were underestimated by the depressive participants. The sadness scores assessed by the Brief Mood Inventory Scale (BMIS) also suggest that the emotional state of sadness in the depressive participants goes some way to explaining their temporal performance. Statistical analyses and modeling of data support the idea according to which these results may be explained by a slowing down of the internal clock in the depressive participants.     

Visual capacities of the owl monkey (Aotus trivirgatus): temporal contrast sensitivity.

Aotus monkeys were tested in a forced-choice discrimination task to determine their ability to discriminate sinusoidally flickering lights varying in temporal frequency and luminance contrast. Under conditions of moderate light adaptation this primate is maximally sensitive to lights flickering at 10 Hz while the highest frequency they can discriminate is about 42 Hz. At very low light levels (10(-5) ft L) maximum sensitivity is for 2.2--5 Hz flicker. The highest flicker rate that could be discriminated under these conditons was about 29 Hz. In comparison to humans tested in the same situation. Aotus monkeys show relatively lower sensitivity to temporal flicker under conditions of light adaptation but relatively higher sensitivity at very low light levels.     

Effects of intracellular K+ and Rb+ on gating of embryonic rat telencephalon Ca(2+)-activated K+ channels.

We have investigated the effects of intracellular K+ and Rb+ on single-channel currents recorded from the large-conductance Ca(2+)-activated K+ (BK) channel of the embryonic rat telencephalon using the inside-out patch-clamp technique. Our novel observation concerns the effects of these ions on rapid flickering of channel openings. Specifically, flicker gating was voltage dependent, i.e., it was reduced by depolarization in the -60 to -10 mV range with equimolar concentrations of K+ ions (150 Ko+/150 Ki+). Removal of Ki+ resulted in significant flickering at all potentials in this voltage range. In other words, the voltage dependence of flicker gating was effectively eliminated by the removal of Ki+. This suggests that a K+ ion entering the channel from the intracellular medium binds, in a voltage-dependent manner, at a site that locks the flicker gate in its open position. No effects of changes in Ki+ were observed on the primary, voltage-dependent gate of the channel. The change in flickering did not cause a change in the mean burst duration, which indicates that the primary gate is stochastically independent of the flicker gate. Intracellular Rb+ can substitute for--and is even more effective than--Ki+ with regard to suppression of flickering. Substitution of Rbi+ for Ki+ also increased the mean burst duration for V > or = -30 mV. Both effects of Rbi+ were removed by membrane hyperpolarization.     

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.     

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 perception of empty and filled time intervals by rats

In Experiment 1, rats were trained in a within-subjects design to discriminate durations of a filled interval, and durations of an empty interval (an unfilled interval marked at the beginning and end by a 500 ms tone). Training and psychophysical testing was conducted with three sets of anchor durations. Rats made more long responses for filled than for empty intervals at signal durations greater than the geometric mean. In Experiment 2, Group Same was trained similarly to the rats in Experiment 1 with the ambient conditions (houselight illumination) remaining the same during the intertrial interval and the empty intervals. Group Different was trained with the houselight turned off during empty and filled intervals. The similarity of ambient conditions during the intertrial interval and the empty intervals did not significantly affect timing. Filled intervals were timed more precisely and they were perceived as longer than empty intervals of the same duration. The psychophysical functions superimposed across anchor duration sets. These results are the first clear evidence of a filled interval illusion in rats, and they suggest that this difference may reflect a clock rate effect (greater for filled intervals) rather than a switch latency effect (slower for empty intervals).     

Timing Rhythms: Perceived Duration Increases with a Predictable Temporal Structure of Short Interval Fillers

Variations in the temporal structure of an interval can lead to remarkable differences in perceived duration. For example, it has previously been shown that isochronous intervals, that is, intervals filled with temporally regular stimuli, are perceived to last longer than intervals left empty or filled with randomly timed stimuli. Characterizing the extent of such distortions is crucial to understanding how duration perception works. One account to explain effects of temporal structure is a non-linear accumulator-counter mechanism reset at the beginning of every subinterval. An alternative explanation based on entrainment to regular stimulation posits that the neural response to each filler stimulus in an isochronous sequence is amplified and a higher neural response may lead to an overestimation of duration. If entrainment is the key that generates response amplification and the distortions in perceived duration, then any form of predictability in the temporal structure of interval fillers should lead to the perception of an interval that lasts longer than a randomly filled one. The present experiments confirm that intervals filled with fully predictable rhythmically grouped stimuli lead to longer perceived duration than anisochronous intervals. No general over- or underestimation is registered for rhythmically grouped compared to isochronous intervals. However, we find that the number of stimuli in each group composing the rhythm also influences perceived duration. Implications of these findings for a non-linear clock model as well as a neural response magnitude account of perceived duration are discussed.     

Antennal sucrose perception in the honey bee (Apis mellifera L.): behaviour and electrophysiology

Physiological mechanisms of antennal sucrose perception in the honey bee were analysed using behavioural and electrophysiological methods. Following sucrose stimulation of the tip of a freely moving antenna, the latency of proboscis extension was 320–340 ms, 80–100 ms after the first activity in muscle M17 controlling this response. When bees were allowed to actively touch a sucrose droplet with one antenna, contacts with the solution were frequent with durations of 10–20 ms and average intervals between contacts of approximately 40 ms. High sucrose concentrations led to short and frequent contacts. The proboscis response and M17 activity were largely independent of stimulus duration and temporal pattern. Taste hairs of the antennal tip displayed spike responses to sucrose concentrations down to at least 0.1%. The first 25 ms of the response were suitable for discrimination of sucrose concentrations. This time interval corresponds to the duration of naturally occurring gustatory stimuli. Sucrose responses between different hairs on the same antenna showed a high degree of variability, ranging from less than five to over 40 spikes per 0.5 s for a stimulus of 0.1% sucrose. This variability of receptor responses extends the dynamic range of sucrose perception over a large range of concentrations.     

Approach behaviour and embryonic visual experience in chicks: studies on the effect of rate of visual flicker

It has been demonstrated that visual stimulation during the latter part of embryonic development will have its effect on subsequent approach behaviour in the chick. Stimulation here had been of a non-specific type, i.e. mere presence or absence of illumination. This study was conducted to see how much specific stimulation like visual flicker applied during the latter part of embryonic development would affect approach to the same or similar stimuli. In experiment 1 extremely slow flicker (6·6 and 20 c/min) was applied to the eggs under incubation. Treatment groups were tested for approach on flickering and non-flickering stimuli after hatching. Results show that exposing the eggs to flicker has an effect on approach behaviour. Groups that received flicker at a rate of 20 c/min approach faster than those which received flicker at the rate of 6·6 c/min. A significant improvement over trials was only found in the group which received flicker of 20 c/min during the embryonic period. In experiment 2 which employed a range of very much faster flicker no significant treatment effects became apparent. These results suggest that visual flicker as embryonic stimulation is effective in priming the embryo to yield better approach performance after hatching. Results of experiment 2 indicate that the effect of flicker as embryonic stimulation may operate over a certain range in affecting subsequent approach performance.     

Matching unrelated stimuli with same discriminative functions: training order effects

Previous research has shown that after training simple discriminations (A1+/A2−, B1+/B2−), bringing these tasks under conditional control (J1–A1, J2–A2) leads to transfer of discriminative control (J1+/J2−) and to generalized matching on the basis of same discriminative functions (e.g. J1–B1, J2–B2). The same occurs when conditional discriminations are trained (D1–E1, D2–E2; F1–G1, F2–G2). When the subjects are then trained to demonstrate correct relations (D1–E1, D2–E2) when given X1 and to demonstrate incorrect relations when given X2 (XD–E), transfer of discriminative control (X1+/X2−) and generalized matching on the basis of same discriminative functions emerges (e.g. X1F1–G1, X2F1–G2). The present study investigated if these performances are dependent on the training and/or testing order. In Experiment 1, the lower-order contingency tasks were trained before the higher-order contingency tasks (A1+/A2−, B1+/B2− before J–A, and D–E, F–G before XD–E). Half the subjects received the J–B test before the more complex XF–G test (Condition A), while for the other subjects, this testing order was reversed (Condition B). Finally, all subjects received additional tests in which they were given the opportunity to demonstrate the discriminative properties of the J and X stimuli (J1+/J2−, X1+/X2−), and to match the A, J, and X stimuli with newly introduced stimuli of same discriminative properties (e.g. J1-POLITE, J2-RUDE). Experiment 2 was the same except that the training order was reversed (J–A before A1+/A2−, B1+/B2−, and XD–E before D–E, F–G). The results were affected by the training order but not by the testing order. Transfer of discriminative functions and generalized matching on the basis of same functions only occurred reliably when the lower-order contingency tasks were trained first. A stimulus-control account of the data is offered.     

The Effects of Stimulus Variability on the Perceptual Learning of Speech and Non-Speech Stimuli

Previous studies suggest fundamental differences between the perceptual learning of speech and non-speech stimuli. One major difference is in the way variability in the training set affects learning and its generalization to untrained stimuli: training-set variability appears to facilitate speech learning, while slowing or altogether extinguishing non-speech auditory learning. We asked whether the reason for this apparent difference is a consequence of the very different methodologies used in speech and non-speech studies. We hypothesized that speech and non-speech training would result in a similar pattern of learning if they were trained using the same training regimen. We used a 2 (random vs. blocked pre- and post-testing) × 2 (random vs. blocked training) × 2 (speech vs. non-speech discrimination task) study design, yielding 8 training groups. A further 2 groups acted as untrained controls, tested with either random or blocked stimuli. The speech task required syllable discrimination along 4 minimal-pair continua (e.g., bee-dee), and the non-speech stimuli required duration discrimination around 4 base durations (e.g., 50 ms). Training and testing required listeners to pick the odd-one-out of three stimuli, two of which were the base duration or phoneme continuum endpoint and the third varied adaptively. Training was administered in 9 sessions of 640 trials each, spread over 4–8 weeks. Significant learning was only observed following speech training, with similar learning rates and full generalization regardless of whether training used random or blocked schedules. No learning was observed for duration discrimination with either training regimen. We therefore conclude that the two stimulus classes respond differently to the same training regimen. A reasonable interpretation of the findings is that speech is perceived categorically, enabling learning in either paradigm, while the different base durations are not well-enough differentiated to allow for categorization, resulting in disruption to learning.     

Critical flicker detection frequency and double pulse recognition threshold do not depend on the spectral properties of stimuli

We have measured the critical flicker detection frequency (CFDF) and double pulse recognition threshold (DPT) using three LEDs with power peaks at 460, 525 and 625 nm for target illumination. Brightness equalization was performed by customized heterochromatic flicker photometry (cHFP). Reference luminance levels were 170 cd/m² (blue LED, 60 subjects), 4 cd/m² (green LED, 20 subjects), and 1 cd/m² (green LED, 20 subjects). The measurement at 1 cd/m² was preceded by 15 min of dark adaptation. The angle of view for the target was 3°, and the duration of stimuli was 1 ms. An experimental pulse generator with three channels and a projector was used. No differences in CFDF at different spectral properties of stimulus were observed at all three levels of luminance. Thus, it is concluded that temporal vision resolution does not depend on the spectral properties of visual stimuli.     

Pigeons' timing of an arbitrary and a naturalistic auditory stimulus: tone versus cooing

Previous animal research has traditionally used arbitrary stimuli to investigate timing in a temporal bisection procedure. The current study compared the timing of the duration of an arbitrary, auditory stimulus (a 500-Hz tone) to the timing of the duration of a naturalistic, auditory stimulus (a pigeon cooing). In the first phase of this study, temporal perception was assessed by comparing psychophysical functions for the duration of tone and cooing signals. In the first set of tests, the point of subjective equality (PSE) was significantly lower for the tone than for the cooing stimulus, indicating that tones were judged longer than equivalent durations of cooing. In the second set of tests, gaps were introduced in the tone signal to match those present in the cooing signal, and no significant difference in the PSE for the tone or the cooing signal was found. A repetition of the testing conducted with gaps removed from the tone signal, failed to replicate the difference in the PSEs for the tone and cooing signals originally obtained. In the second phase of the study, memory for the duration of tone and cooing was examined, and a choose-long bias was found for both signals. Based on these results, it appears that, for pigeons, there may be no significant differences in either temporal perception or temporal memory for arbitrary, auditory signals and more complex, naturalistic, auditory signals.     

Neural Bases for Individual Differences in the Subjective Experience of Short Durations (Less than 2 Seconds)

The current research was designed to establish whether individual differences in timing performance predict neural activation in the areas that subserve the perception of short durations ranging between 400 and 1600 milliseconds. Seventeen participants completed both a temporal bisection task and a control task, in a mixed fMRI design. In keeping with previous research, there was increased activation in a network of regions typically active during time perception including the right supplementary motor area (SMA) and right pre-SMA and basal ganglia (including the putamen and right pallidum). Furthermore, correlations between neural activity in the right inferior frontal gyrus and SMA and timing performance corroborate the results of a recent meta-analysis and are further evidence that the SMA forms part of a neural clock that is responsible for the accumulation of temporal information. Specifically, subjective lengthening of the perceived duration were associated with increased activation in both the right SMA (and right pre-SMA) and right inferior frontal gyrus.     

Differential effects of empty and filled intervals on duration estimation by pigeons: tests of an attention-sharing explanation

Pigeons were trained in a within-subjects design to discriminate durations of an empty interval and a filled interval. Even when different stimuli were used to mark empty intervals and to signal filled intervals, pigeons judged empty intervals to be longer than equal-length filled intervals. This timing difference was not a result of pigeons timing marker duration on empty interval trials. Increasing marker duration did not produce an overestimation of the empty time intervals. It was suggested that this timing difference could be due to a reduction in attention to temporal processing on filled interval trials when visual stimuli are used. Consistent with this hypothesis, it was found that empty intervals were judged longer than filled intervals when testing occurred in a darkened test room, but not when the test room was illuminated. In addition, no timing difference was observed when different auditory stimuli were used as markers for empty intervals and as signals for filled intervals.