Systematic nonlinearities in the memory representation of time.

The representation of time was investigated by testing rats with intervals that changed by 2 s across trials. In Experiment 1, 2 ranges (20–150 s, 30–160 s; n?=?10 rats per group) were examined. The times at which response bursts occurred (start time) were approximately proportional to interval durations. However, systematic departures from linearity were observed. Nonlinearities were related to the absolute duration of intervals, rather than to durations relative to the range. In Experiment 2, 660-s trials were inserted into the sequence of intervals (10–140 s, n?=?20). Start and end times of response bursts were approximately proportional to intervals, but nonlinearities in start and end times were correlated, indicating that the source of nonlinearity was in the memory representation of time rather than in a decision process. These results indicate that the representation of time is nonlinearly related to physical time. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Temporal search as a function of the variability of interfood intervals.

We attempted to determine whether timing theories developed primarily to explain performance in fixed-interval reinforcement schedules are also applicable to variable intervals. Groups of rats were trained in lever boxes on peak procedures with a 30-, 45-, or 6O-s interval, or a 30- to 6O-s uniform distribution (Experiment 1); a 60-s fixed and 1- to 121-s uniform distribution between and within animals (Experiment 2); and a procedure in which the interval between food and next available food gradually changed from a fixed 60 s to a uniform distribution between 0 and 120 s (Experiment 3). In uniform interval schedules rats made lever responses at particular times since food, as measured by the distribution of food-food intervals, the distribution of postreinforcement pauses, and the mean response rate as a function of time since food. Qualitative features of this performance are described by a multiple-oscillator connectionist theory of timing. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Dynamics of time discrimination: II. The effects of multiple impulses

According to a diffusion generalization model, time discrimination is determined by the frequency and recency of preceding intervals of time. A procedure for studying rapid timing was used to investigate whether pigeons' wait-time responses were sensitive to these factors. In Experiment 1 the number (two or eight) and spacing (consecutive or far apart) of 5-s interfood intervals (called impulses) intercalated in a series of 15-s interfood intervals (nonimpulses) were studied. Experiment 2 was identical to the first but the interfood intervals were increased by a factor of three. Overall, impulses shortened wait times in the next interfood interval. However, several impulses occurring in succession extended the localized effect of an impulse: Wait times following a set of eight-close impulses were slow to recover to preimpulse levels. The results show that linear waiting is only an approximation to the dynamic process, and a process that is sensitive to events in an animal's remote past, such as the diffusion generalization model, provides a better account of rapid timing effects.     

Stimulus and temporal cues in classical conditioning.

In 2 experiments, separate groups of rats were given stimulus conditioning, temporal conditioning, untreated control and (in Experiment 2) learned irrelevance control procedures followed by a compound with both stimulus and temporal cues. Stimulus conditioning consisted of a random 15-s duration conditioned stimulus (CS) followed by food; temporal conditioning consisted of food–food intervals of fixed 90 s (Experiment 1) or fixed 75?+?random 15 s (Experiment 2). The stimulus group abruptly increased responding after CS onset, and the temporal group gradually increased responding over the food–food interval. When the food–food interval was fixed 90 s, the temporal cue exerted stronger control in the compound, whereas when the food–food interval was fixed 75?+?random 15 s, the stimulus cue exerted stronger control. The strength of conditioning, temporal gradients of responding, and cue competition effects appear to reflect simultaneous timing of multiple intervals. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Piezoelectric and related properties of hydrated collagen

Two piezoelectric constants (polarization per unit stress, d=d'-id', and polarization per unit strain, e=e'-ie'), the elastic constant, and dielectric constant are determined for oriented collagen at different hydration levels at 10 Hz from -150 to 50 degrees C. With no hydration (approximately 0% H2O), d' increases slightly with higher temperatures, while e' decreases slightly. Near 11 wt% H2O, both d' and e' increase then decrease around 0 degrees C, and is probably caused by an increase of the dielectric constant and the ionic conductivity in the nonpiezoelectric phase. Hydration greater than 25 wt%, d' and e' decrease above -50 degrees C which is considered to be due to a greater ionic conductivity surrounding the piezoelectric phase.     

The coupled oscillator model of between-hand coordination in alternate-hand tapping: A reappraisal.

Single and alternating hand tapping were compared to test the hypothesis that coordination during rhythmic movements is mediated by the control of specific time intervals. In Experiment 1, an auditory metronome was used to indicate a set of timing patterns in which a 1-s interval was divided into 2 subintervals. Performance, measured in terms of the deviation from the target patterns and variability, was similar under conditions in which the finger taps were made with 1 hand or alternated between the 2 hands. In Experiment 2, the modality of the metronome (auditory or visual) was found to influence the manner in which the produced intervals deviated from the target patterns. These results challenge the notion that bimanual coordination emerges from coupling constraints intrinsic to the 2-hand system. They are in accord with a framework that emphasizes the control of specific time intervals to form a series of well-defined motor events. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Scalar timing in temporal generalization in humans with longer stimulus durations

Three experiments investigated temporal generalization performance in humans by using stimulus durations similar to those previously used with rats. In most conditions, chronometric counting was prevented by concurrent shadowing of temporally irregular numbers. Experiment 1 examined performance with visual stimuli, when the standard was 4.0 s long and nonstandard stimuli were spaced either linearly or logarithmically around the standard. Generalization gradients were asymmetrical with linear spacing but symmetrical with logarithmic spacing, a result obtained previously with humans. Experiment 2 used auditory stimuli and varied the standard across values of 2.0, 4.0, 6.0, and 8.0 s. All gradients were asymmetrical, and good superposition was obtained, indicating conformity to scalar timing. Experiment 3 prevented or encouraged chronometric counting by changing instructions, and temporal generalization gradients differed when counting was and was not used.     

Revising the redundancy principle in multimedia learning.

College students viewed a short multimedia PowerPoint presentation consisting of 16 narrated slides explaining lightning formation (Experiment 1) or 8 narrated slides explaining how a car's braking system works (Experiment 2). Each slide appeared for approximately 8-10 s and contained a diagram along with 1-2 sentences of narration spoken in a female voice. For some students (the redundant group), each slide also contained 2-3 printed words that were identical to the words in the narration, conveyed the main event described in the narration, and were placed next to the corresponding portion of the diagram. For other students (the nonredundant group), no on-screen text was presented. Results showed that the group whose presentation included short redundant phrases within the diagram outperformed the nonredundant group on a subsequent test of retention (d = 0.47 and 0.70, respectively) but not on transfer. Results are explained by R. E. Mayer's (2001, 2005a) cognitive theory of multimedia learning, in which the redundant text served to guide the learner's attention without priming extraneous processing. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Circadian time perception.

The variability of anticipating a meal was investigated. Sprague-Dawley rats earned food by inspecting a food source during a 3-hr interval. Food was not available at other times. In Experiment 1, the meal started 3 or 7 hr after light offset in a 12-hr light-dark cycle. Experiment 2 was conducted in constant darkness with 14-, 22-, 22.5-, 24-, 25.5-, 26-, or 34-hr intermeal intervals. Inspections increased before the meal. Rats timed intervals in the circadian range (22–26 hr) with lower variability than that for intervals outside this range (3–14 and 34 hr). Higher precision in timing selected intervals violates the scalar property. Proximity to a circadian oscillator improves timing precision. Variability may be used to identify oscillators with noncircadian periods. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Time perception and reproduction in young adults with attention deficit hyperactivity disorder.

Adults with attention deficit hyperactivity disorder (ADHD; n ?=? 104) were compared with a control group (n ?=? 64) on time estimation and reproduction tasks. Results were unaffected by ADHD subtype or gender. The ADHD group provided larger time estimations than did the control group, particularly at long intervals. This became nonsignificant after controlling for IQ. The ADHD group made shorter reproductions than the control group (15- and 60-s intervals) and greater reproduction errors (12-, 45-, 60-s durations). These differences remained after controlling for IQ and comorbid oppositional defiant disorder, depression, and anxiety. Only the level of anxiety contributed to errors (at 12-s duration) beyond the level of ADHD. Results extended findings on time perception in ADHD children to adults and ruled out comorbidity as the basis of the errors. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Role of temporal order and odor intensity in taste-potentiated odor aversions.

The role of the temporal order of odor and taste was studied in two experiments, and a third experiment studied the role of odor intensity in flavor-toxicosis conditioning with thirsty rats licking water spouts in a "wind tunnel." In all experiments, odors and tastes were presented for 2 min to rats, and 30 min later, a toxin (lithium chloride) was intubated. In Experiment 1, an odor was presented 90 s before, during, or 90 s after a taste to independent groups. Experiment 2 was a within-subjects partial replication of the first. Each rat was presented with one odor, then a taste, then a second odor with each stimulus separated by 45 s. The results of Experiments 1 and 2 indicated that (a) odor alone is not associated with illness under our conditions, (b) presenting an odor and a taste at the same time potentiates the odor component so that it is associated with illness, (c) 45-s and 90-s intervals between odor and taste eliminate potentiation, and (d) taste and odor interact asymmetrically; that is, odor has little effect on the development of taste-illness associations. In Experiment 3, an odor and a taste were presented simultaneously, and odor intensity varied. As odor intensity increased, the strength of the taste-potentiated odor aversion increased, whereas the aversion to the taste remained constant. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Timing for the absence of a stimulus: The gap paradigm reversed.

Contrary to data showing sensitivity to nontemporal properties of timed signals, current theories of interval timing assume that animals can use the presence or absence of a signal as equally valid cues as long as duration is the most predictive feature. Consequently, the authors examined rats' behavior when timing the absence of a visual or auditory stimulus in trace conditioning and in a "reversed" gap procedure. Memory for timing was tested by presenting the stimulus as a reversed gap into its timed absence. Results suggest that in trace conditioning (Experiment 1), rats time for the absence of a stimulus by using its offset as a time marker. As in the standard gap procedure, the insertion of a reversed gap was expected to "stop" rats' internal clock. In contrast, a reversed gap of 1, 5-, or 15-s duration "reset" the timing process in both trace conditioning (Experiment 2) and the reversed gap procedure (Experiment 3). A direct comparison of the standard and reversed gap procedures (Experiment 4) supported these findings. Results suggest that attentional mechanisms involving the salience or content of the gap might contribute to the response rule adopted in a gap procedure. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Simultaneous timing of multiple intervals: Implications of the scalar property.

Three experiments with pigeons are reported in which the scalar property in simultaneous timing tasks was studied. According to scalar expectancy theory, the scalar property should be maintained in simultaneous timing, but the behavioral theory of timing predicts that the scalar property should be evident only in independent timing. Experiment 1 showed that the appearance of distinct peaks at reinforcement times required about a 4:1 ratio between intervals. Experiment 2 (2-interval timing task) and Experiment 3 (3-interval timing task) used an individual trial analysis technique to examine high-rate responding segments bracketing the times of reinforcement. The standard deviations of the starting and stopping times of high-rate segments were linearly related to their means and to reinforcement time, supporting the scalar property in simultaneous timing. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Timing light and tone signals in pigeons.

Pigeons' ability to time light and tone stimuli was examined in four experiments. In Experiment 1, two groups of pigeons were trained to discriminate between 2- and 8-s durations of lights or tones and then were transferred to reversal or nonreversal discriminations in the alternate modality. Pigeons learned the light discrimination faster than the tone discrimination and showed immediate positive intermodal transfer from tone to light but not from light to tone. In Experiments 2–4, the peak procedure was used to study birds' timing of 15- and 30-s fixed-interval light and tone signals. Peak times on empty trials under baseline conditions closely approximated the length of fixed-interval signals. When pigeons were tested with time-outs and intermodal switches introduced midway through an empty trial, they tended to reset the timing mechanism and begin timing again from 0 s. With both estimation and production procedures, pigeons were less accurate when timing the tone stimuli than when timing the light stimuli. A comparison of these data with data from timing experiments with rats suggests several possible differences in timing processes between pigeons and rats. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The Effects of Spatial Stimulus-Response Compatibility on Choice Time Production Accuracy and Variability.

Five experiments examined the relations between timing and attention using a choice time production task in which the latency of a spatial choice response is matched to a target interval (3 or 5 s). Experiments 1 and 2 indicated that spatial stimulus-response incompatibility increased nonscalar timing variability without affecting timing accuracy and that choice reaction time practice reduced choice time production variability. These data support a "temporal discounting" model in which response choice and timing occur in series, but the interval timed is shortened to account for nontemporal processing. In Experiment 3, feedback and anticipation task demands improved choice time production accuracy. In Experiments 4 and 5, the delay between the start-timing and choice-decision signals interacted with choice difficulty to affect choice time production accuracy and variability when timing a 3- but not a 5-s interval, suggesting that attention mediates timing before and after an interruption in timing. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Electrophysiological characterization of 5-HT receptors on rat petrosal neurons in dissociated cell culture

The petrosal ganglion supplies chemoafferent pathways via the glossopharyngeal (IXth) nerve to peripheral targets which release various neurotransmitters including serotonin (5-HT). Here, we combined rapid 5-HT application with patch clamp, whole-cell recording to investigate whether 5-HT receptors are expressed on isolated petrosal neurons (PN), cultured from 7-12 day-old rat pups. In responsive cells, the dominant effect of 5-HT was a rapid depolarization associated with a conductance increase in approximately 43% of the neurons (53/123); however, in a minority population ( approximately 6%; 8/123), 5-HT caused membrane depolarization associated with a conductance decrease. In the former group, 5-HT produced a transient inward current (I5-HT) in neurons voltage-clamped near the resting potential ( approximately -60 mV); the effect was mimicked by the 5-HT3 receptor-specific agonist, 2-methyl-5-HT, suggesting it was mediated by 5-HT3 receptors. Further, I5-HT was selectively inhibited by the 5-HT3 receptor-specific antagonist MDL72222 (1-10 microM), but was unaffected by either 5-HT1/5-HT2 receptor antagonist, spiperone, or by 5-HT2 receptor-specific antagonist, ketanserin (50-100 microM). I5-HT displayed moderate inward rectification and had a mean reversal potential (+/-S.E.M.) of -4.3+/-6.6 mV (n=6). Application of 5-HT (dose range: 0.1-100 microM) produced a dose-response curve that was fitted by the Hill equation with EC50= approximately 3.4 microM and Hill coefficient= approximately 1.6 (n=8). The activation phase of I5-HT (10 microM 5-HT at -60 mV) was well fitted by a single exponential with mean (+/-S.E.M.) time constant of 45+/-30 ms (n=6). The desensitization phase of I5-HT was best fitted by a single exponential with mean (+/-S.E.M.) time constant of 660+/-167 ms (n=6). Fluctuation analysis yielded an apparent mean single-channel conductance (+/-S.E.M) of 2.7+/-1.5 pS (n=4) at -60 mV. In the minority ( approximately 6%) population of neurons which responded to 5-HT with a conductance decrease, the depolarization was blocked by the 5-HT2 receptor antagonist, ketanserin (50 microM). Taken together, these results suggest that 5-HT3 receptors are the major subtype expressed by rat petrosal neurons, and therefore are candidates for facilitating chemoafferent excitation in response to 5-HT released from peripheral targets.     

Faster adjustment of O2 delivery does not affect V(O2) on-kinetics in isolated in situ canine muscle

The mechanism(s) limiting muscle O2 uptake (VO2) kinetics was investigated in isolated canine gastrocnemius muscles (n = 7) during transitions from rest to 3 min of electrically stimulated isometric tetanic contractions (200-ms trains, 50 Hz; 1 contraction/2 s; 60-70% of peak V(O2)). Two conditions were mainly compared: 1) spontaneous adjustment of blood flow (Q) [control, spontaneous Q (C Spont)]; and 2) pump-perfused Q, adjusted approximately 15 s before contractions at a constant level corresponding to the steady-state value during contractions in C Spont [faster adjustment of O2 delivery (Fast O2 Delivery)]. During Fast O2 Delivery, 1-2 ml/min of 10(-2) M adenosine were infused intra-arterially to prevent inordinate pressure increases with the elevated Q. The purpose of the study was to determine whether a faster adjustment of O2 delivery would affect V(O2) kinetics. Q was measured continuously; arterial (Ca(O2)) and popliteal venous (Cv(O2)) O2 contents were determined at rest and at 5- to 7-s intervals during contractions; O2 delivery was calculated as Q x Ca(O2), and V(O2) was calculated as Q x arteriovenous O2 content difference. Times to reach 63% of the difference between baseline and steady-state VO2 during contractions were 23.8 +/- 2.0 (SE) s in C Spont and 21.8 +/- 0.9 s in Fast O2 Delivery (not significant). In the present experimental model, elimination of any delay in O2 delivery during the rest-to-contraction transition did not affect muscle V(O2) kinetics, which suggests that this kinetics was mainly set by an intrinsic inertia of oxidative metabolism.     

Interval timing accuracy and scalar timing in C57BL/6 mice.

In many species, interval timing behavior is accurate—appropriate estimated durations—and scalar—errors vary linearly with estimated durations. Whereas accuracy has been previously examined, scalar timing has not been clearly demonstrated in house mice (Mus musculus), raising concerns about mouse models of human disease. The authors estimated timing accuracy and precision in C57BL/6 mice, the most used background strain for genetic models of human disease, in a peak-interval procedure with multiple intervals. Both when timing 2 intervals (Experiment 1) or 3 intervals (Experiment 2), C57BL/6 mice demonstrated varying degrees of timing accuracy. An important finding was that, both at the individual and group levels, their precision varied linearly with the subjective estimated duration. Further evidence for scalar timing was obtained using an intraclass correlation statistic. This is the first report of consistent, reliable scalar timing in a sizable sample of house mice, thus validating the peak-interval procedure as a valuable technique, the intraclass correlation statistic as a powerful test of the scalar property, and the C57BL/6 strain as a suitable background for behavioral investigations of genetically engineered mice modeling disorders of interval timing. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Categorical scaling of time: Implications for clock-counter models.

Pigeons partitioned time into three intervals. Responses to one key could be reinforced after a short time, to a second key after an intermediate time, and to a third key after a long time. The values of the short, intermediate, and long times and the proportion of trials ending with reinforcement were varied. Absolute and relative response rates on each key were an orderly function of time and showed approximately proportional changes with changes in the interval values, consistent with Weber's law, Gibbon's (1977) scalar expectancy theory, and Killeen and Fetterman's (1988) behavioral theory of timing (BeT). Standard deviations of the times at which subjects switched between successive keys increased more slowly within a condition than across conditions, as predicted by BeT. Increases and decreases in reinforcement probability produced both transient and longer lasting changes in timing behavior, once again, in accord with predictions of BeT. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Internal clock processes and the filled-duration illusion.

In 3 experiments, the authors compared duration judgments of filled stimuli (tones) with unfilled ones (intervals defined by clicks or gaps in tones). Temporal generalization procedures (Experiment 1) and verbal estimation procedures (Experiments 2 and 3) all showed that subjective durations of the tones were considerably longer than those of unfilled intervals defined either by clicks or gaps, with the unfilled intervals being judged as approximately 55%-65% of the duration of the filled ones when real duration was the same. Analyses derived from the pacemaker-switch-accumulator clock model incorporated into scalar timing theory suggested that the filled/unfilled difference in mean estimates was due to higher pacemaker speed in the former case, although conclusively ruling out alternative interpretations in terms of attention remains difficult. (PsycINFO Database Record (c) 2010 APA, all rights reserved)