Two-step acquisition: Modification of an internal clock's criterion.

10 male albino Norway rats were trained on a discrete-trial peak procedure in which food, if available, occurred following the 1st response after a signal had been present for 10 sec. 10 other Ss were trained on the same procedure with a 20-sec criterion. When the time of reinforcement was reversed between groups, Ss adjusted their temporal criterion in 2 abrupt steps. During the intermediate state of the 3-step function, Ss used a temporal criterion that was near the geometric mean of the initial and terminal times of reinforcement. It is concluded that the intermediate transition state reflects an internal structure in the animal's information processing system not readily accounted for by stimulus–response models of behavior. (35 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Hippocampus, time, and memory.

Five experiments determined the effects of hippocampal damage on timing and the memory for temporal events. Norway rats (N?=?20) were trained to discriminate between auditory signals that differed in both duration (2 or 8 sec) and rate (2 or 16 cycles/sec). After Ss acquired the discrimination, signals with intermediate durations and rates were presented. Ss then received either fimbria-fornix lesions or control operations. Postoperatively, the accuracy of duration and rate discriminations as measured by the difference limen (DL) was unaffected by the lesion, but the point of subjective equality was shifted to a shorter duration and a slower rate by the lesion. Both Ss with lesions and Ss with control operations showed cross-modal transfer of duration and rate from the auditory signals used in training to visual signals. When a 5-sec delay was imposed between the end of a signal and the opportunity to respond, lesioned Ss were selectively impaired by the addition of the delay as measured by an increase in the DL. When a peak procedure was employed, the maximum response rate of controls was approximately at the time of scheduled reinforcement (20 sec), but the maximum response rate of lesioned Ss was earlier than the time of reinforcement. When a 5-sec gap was imposed in the signal, controls summed the signal durations before and after the gap, whereas lesioned Ss showed no retention of the signal duration prior to the gap. Lesions impaired spatial working memory in an 8-arm radial maze. (51 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Comparison of timing and classical conditioning.

Four experiments with 63 Charles River and Sprague-Dawley rats investigated whether the timing of a stimulus (sound) correlated with the strength of a CR to the stimulus. The timing (effective duration) of the stimulus was measured with the peak procedure, similar to a discrete-trials, fixed-interval procedure. Ss were trained so that their response rate reached a maximum at approximately 40–60 sec after the onset of a light; the time of the maximum measured from the start of the light (peak time) was the measure of timing. On some trials, the light was preceded by a short (5-sec) or long (20- or 30-sec) interval of sound. It was assumed that the difference in peak time after long and short sounds reflected the timing of the sound: If the sound was timed, the longer sound would produce a lower peak time; if the sound was not timed, the 2 durations of sound would produce the same peak time. The CR was leverpressing during the sound. The sound was treated in various ways: presented alone (Exps I, III, and IV), followed by food (Exps I, III, and IV), preceded by food (Exp III), and followed by food after 20-sec (Exp IV). Treatments that produced no timing of sound produced no CR, and treatments that increased (or decreased) timing also increased (or decreased) the CR. Findings suggest that there is overlap between the mechanisms that produce time discrimination and the mechanisms that produce classical conditioning. (41 ref) (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Cross-modal use of an internal clock.

Used time-discrimination procedures with male albino Charles River rats to determine if light and sound are timed by the same internal clock and if measured durations of light and sound are stored in the same memory. Exp I used a choice procedure and a cross-modal transfer-of-training design. There was transfer of the time discrimination across modalities: To some extent, Ss treated the new signal (sound) as if it were the old signal (light). Exp II (6 experienced Ss) showed that changing the time of food during light (or sound) changed peak time during sound (or light). In Exps III and IV, intervals of light (or sound) were followed by intervals of sound (or light). The interval of light decreased the peak time measured from the start of the interval of sound, whether the 2 intervals were adjacent or separated by 5 sec. The longer the 1st interval, the greater the decrease. Findings suggest that measured durations of light and sound are stored by the same memory and that light and sound are timed by the same clock. (33 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

What starts an internal clock?

Five experiments with 52 male Charles River CD rats investigated under what conditions a stimulus is timed by the internal clock used in time-discrimination procedures. In Exps I–IV, Ss were trained to time one stimulus (e.g., light) and then tested as to whether they timed a stimulus from another modality (e.g., sound). The 2nd stimulus was treated in 3 ways: exposed (presented alone), paired with food, and extinguished. Exps I and II used the peak procedure, similar to a discrete-trial FI schedule, and paired the treated stimulus with food using instrumental training; Exps III and IV used a psychophysical choice procedure and paired the treated stimulus with food using classical conditioning. All 4 experiments found that there was cross-modal transfer of the time discrimination after pairing but not after exposure or extinction. This suggests that Ss' internal clock timed the treated stimulus after pairing but not after exposure or extinction. Exp V suggested that the decline of responding observed in extinction was not due to changes in timing. Thus, the internal clock apparently times stimuli with signal value (associative strength) and does not time stimuli without signal value. (46 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Abstraction of temporal attributes.

Four experiments demonstrated cross-modal transfer (CMT) of classification rules for temporal intervals. In Exp I, 20 male albino Norway rats learned a temporal discrimination between a 2- and an 8-sec signal in one modality (vision or audition). Results show positive transfer to a temporal discrimination between a 2- and an 8-sec signal in the other modality when the response rule was maintained, and negative transfer when the response rule was reversed. Exp II with 20 Ss demonstrated positive CMT in a temporal generalization procedure. Exp III demonstrated CMT of both duration and temporal location in a procedure in which 20 Ss were exposed to 3 successive signal durations. Exp IV demonstrated CMT of both duration and temporal order in a procedure in which 5 Ss were exposed to simultaneously presented signal durations, one auditory and one visual. It is concluded that rats can abstract temporal attributes from modality-specific aspects of a signal. (38 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Postreinforcement signal processing.

Demonstrated postreinforcement signal processing by male albino Norway rats (N?=?262) in 6 experiments, using a discrete-trials choice procedure. Exp I assessed the extent to which Ss were able to transfer knowledge about associations between postreinforcement signal durations and choice responses to conditions in which a particular signal duration preceded the opportunity to make a choice response. In Exp II, the generality of the transfer effect was demonstrated by using both signal duration and signal modality as relevant stimulus attributes for the postreinforcement signals. The role of the relative durations of the reinforcement-signal gap and the intertrial interval was investigated in Exp III. To assess the effects of within- and between-trial signal relations on the acquisition of a temporal discrimination, both pre- and postreinforcement signals were presented on each trial in Exps IV and V. The effects of pre- and postreinforcement signal relations on the steady-state performance of a temporal bisection task across 3 signal ranges were studied in Exp VI. Overall results suggest that rats readily process various stimulus attributes of postreinforcement signals and that relations among postreinforcement signals, choice responses, and prereinforcement signals are major determinants of choice behavior. (39 ref) (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Operant responding and stimulus control in tawny owls (Strix aluco).

Trained 2 tawny owls to make a bar-pecking response, reinforced by the presentation of small cubes of ox heart. Ss readily acquired the response, and their pattern of responding under fixed-ratio, variable-ratio, and VI schedules of reinforcement were similar to the typical response patterns of other species. Stimulus control was demonstrated in 3 Ss by training them to simultaneously discriminate between horizontally and vertically striped patterns. A high degree of control was obtained in all Ss. However, a small increase in the spatial separation of stimulus and response resulted in a considerable loss of stimulus control, suggesting that it would be difficult to employ the tracking method of threshold determination with this species. (15 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Alteration of classically conditioned heart rate by operant reinforcement in monkeys.

Ran 6 adolescent male rhesus monkeys alternately on classical conditioning and on operant heart rate training schedules. The classical unconditioned stimulus (UCS) was identical to the operant negative reinforcement. After operant training, some Ss changed their heart rate responses to the classical conditioned stimulus (CS). When both the operant and the classical schedules were in force simultaneously, all Ss changed their previous heart rate responses to the classical CS without significantly changing their blood pressure responses to this stimulus. The changes in heart rate response to the CS sometimes persisted long after the operant schedules were no longer in force. These results show that a classically conditioned response can be altered by operant reinforcement, and they suggest that the classical UCS actually may be an operant reinforcer. (29 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Learning the temporal dynamics of behavior.

This study presents a dynamic model of how animals learn to regulate their behavior under time-based reinforcement schedules. The model assumes a serial activation of behavioral states during the interreinforcement interval, an associative process linking the states with the operant response, and a rule mapping the activation of the states and their associative strength onto response rate or probability. The model fits data sets from fixed-interval schedules, the peak procedure, mixed fixed-interval schedules, and the bisection of temporal intervals. The major difficulties of the model came from experiments that suggest that under some conditions animals may time 2 intervals independently and simultaneously. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Vigilance performance under conditions of redundant and nonredundant signal presentation.

Brief interruptions in a sound, a light, or both the sound and light, were monitored by 41 Ss over a 3-hour period. A dual response apparatus allowed the Ss to report the light signals, the sound signals, or both. The detection rate was found to be significantly better for the redundant signals than for either alone. While the detectability of each component of the redundant signal was comparable to its corresponding single mode, a systematic deviation in the bimodal curve—from predicted to observed—was noted. It was concluded that the weaker component of a redundant signal contributes significantly to the overall detectability, and the use of dual channel displays in applied vigilance situations is justified. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Temporal integration in duration and number discrimination.

Investigated temporal integration in duration and number discrimination among 6 male albino rats through the use of a psychophysical choice procedure. A response on 1 lever ("short" response) following a 1-sec white-noise signal (WNS) was followed by food reinforcement, and a response on the other level ("long" response) following a 2-sec WNS was also followed by food reinforcement. Either response following a signal of 1 of 5 intermediate durations was unreinforced. This led to a psychophysical function in which the probability of a long response was related to signal duration in an ogival manner. On 2 test days, a WNS with 5, 6, 7, 8, or 10 segments of either 0.5-sec on and 0.5-sec off or 1-sec on and 1-sec off was presented, and a choice response following these signals was unreinforced. The probability of a long response was the same function of a segmented signal and a continuous signal if each segment was considered equivalent to 200 msec. A quantitative fit of scalar estimation theory suggested that the latencies to initiate temporal integration and to terminate the process are both about 200 msec and that the same internal accumulation process can be used for counting and timing. (16 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Retention and acquisition of classical trace conditioned responses by rabbits with hippocampal lesions.

Examined the effects of dorsal hippocampal lesions on retention of classical trace conditioned responses (CRs) using the rabbit nictitating membrane preparation. In Exp I, 18 New Zealand albino rabbits were trained to criteria and then lesioned either in the cortex or in the hippocampus and the cortex. Hippocampal damage had no effect on the retention of responses but produced significantly longer onset latencies. A control group of hippocampal Ss acquired CRs at least as quickly as the prelesion Ss and exhibited longer response onset latency. Exp II, with 24 Ss, evaluated the performance of hippocampal-lesioned Ss in classical trace conditioning with either a low-intensity periorbital shock or a corneal air puff as the unconditioned stimulus (UCS). Hippocampal Ss successfully acquired CRs under both conditions but exhibited an alteration of response onset that depended on the form of the UCS. Hippocampal Ss displayed shorter response onset in the air-puff condition and longer response onset in the shock condition. Cortical Ss consistently timed responses regardless of the UCS. Findings suggest that the hippocampus modulates temporal characteristics of learned behavior. (37 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Motor coactivation revealed by response force in divided and focused attention.

Four experiments examined effects of bimodal stimulation on response force (RF) in addition to reaction time (RT). In a divided-attention task (Exps 1–3), Ss were asked for a speeded response to either a visual or an auditory signal. In unimodal signal trials, either a visual or auditory signal was presented alone, and in redundant-signals trials, both signals were presented simultaneously. The same stimulus arrangement was used in a focused-attention task (Exp 4), but Ss had to withhold their response when an auditory signal was presented alone. In all experiments, the fastest RTs were attained in redundant-signals trials. In addition, RF was largest in redundant-signals trials, especially in the divided-attention task, suggesting a motor coactivation hypothesis. The results indicate that the type of stimulation influences not only when a response is initiated but also how the response is executed. This finding challenges the view, commonly held in mental chronometry, that late motoric processes remain untouched by experimental manipulations. A detailed analysis of the relationship between RT and RF revealed that these variables are not inherently redundant measures, and therefore, RF recording may supplement the traditional RT measurement in mental chronometry. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Concurrent learning of temporal and spatial sequences.

In a serial reaction time task, stimulus events simultaneously defined spatial and temporal sequences. Responses were based on the spatial dimension. The temporal sequence was incidental to the task, defined by the response-to-stimulus intervals in Experiment 1 and stimulus onset asynchronies in Experiment 2. The two sequences were either of equal length and correlated or of unequal length. In both experiments, spatial learning occurred regardless of sequence length condition. In contrast, temporal learning occurred only in the correlated condition. These results suggest that timing is an integrated part of action representations and that incidental learning for a temporal pattern does not occur independently from the action. Interestingly, sequence learning was enhanced in the correlated condition, reflecting the integration of spatial-temporal information. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Persistence of negative priming: II. Evidence for episodic trace retrieval.

Responses to recently ignored stimuli may be slower or less accurate than to new stimuli. This negative priming effect decays over time when delay is randomized within Ss, but not when delay varies between Ss. In Exp 1, response–stimulus intervals (RSI) of 500 and 4,000 msec were randomized within Ss in a target localization task. Negative priming of ignored locations diminished with longer delay. However, no significant decay was obtained when RSI and the preceding RSI were equal. Similar results were obtained when RSI and preceding RSI were deliberately confounded by blocking (Exp 2). Negative priming appears to depend on temporal discriminability of the priming episode. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Averaging of temporal memories by rats.

Rats were trained on a mixed fixed-interval schedule in which stimulus A (tone or light) indicated food availability after 10 s and stimulus B (the other stimulus) indicated food availability after 20 s. Testing consisted of nonreinforced probe trials in which the stimulus was A, B, or the compound AB. On single-stimulus trials, rats responded with a peak of activity around the programmed reinforced time. On compound-stimulus trials, rats showed a single scalar peak of responding at a time midway between those for stimulus A and B. These results suggest that when provided with discrepant information regarding the temporal predictability of reinforcement, rats compute an average of the scheduled reinforcement times for the A and B stimuli and use this average to generate an expectation of reward for the compound stimuli. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Changes in energy expenditure and work during response acquisition in rats.

The principle of least effort predicts that behavior will tend to maximum efficiency. To test this prediction, changes in the energy expended (VO?) and work performed per reinforcement were monitored continuously as rats learned to press a beam with a criterion force for liquid food rewards. All 12 Ss exhibited significant decreases in energy expended per reinforcement over the 16 days of observation. Of these, 10 Ss also decreased the work performed per reinforcement. Analyses of motor performance were undertaken to determine how motor programs for changing efficiency were generated. The 10 Ss showing decreased work reinforcement also exhibited significant decreases in the variability of temporal and kinetic response features and in mean response magnitude as a function of practice. Adjustments in work output were primarily accomplished by modifying temporal response features. The kinetic features remained relatively constant for these animals. The remaining 2 Ss differed in that response recruitment increased after Day 9. (PsycINFO Database Record (c) 2010 APA, all rights reserved)