Effect of presentation procedure on taste intensity functions

Magnitude estimations were made for the taste intensity of sodium chloride (NaCl) and quinine sulfate (QSO₄) presented by three different methods: sip, anterior dorsal tongue flow, and whole-mouth flow. Power functions fitted to the data indicate that, for the anterior tongue stimulus (NaCl), the two flowing procedures produced lower exponents than did the sip procedure. For the posterior tongue stimulus (QSO₄), the exponent obtained with dorsal tongue flow was lower than the exponents obtained with either of the whole-mouth procedures, sip or flow. The results are compared to previous experiments on ratio scaling of taste intensity to elucidate the effects of several procedural variables.     

Adaptation and cross-adaptation of the four gustatory qualities

On the basis of magnitude estimations of solutions of NaCl, quinine sulfate, sucrose, and HCl, a seven-step series of each compound was chosen. The concentration of each compound in the same ordinal position of the series was of approximately the same sensory magnitude. The middle concentration of each series was presented as an adapting stimulus, and the entire series was used to test the effects of 2 min of adaptation on magnitude estimations and quality reports. Both NaCl and sucrose adaptation markedly lowered magnitude estimations of test stimuli of the same compounds for concentrations lower than that of the adapting stimulus, but had little effect on higher concentrations. Cross-adaptation generally enhanced the magnitude estimations over those obtained in initial estimations. Neither adaptation nor cross-adaptation procedures produced quality changes.     

Taste thresholds in college-age smokers and nonsmokers

Taste detection thresholds were measured for NaCl and Dulcin and recognition thresholds for NaCl, sucrose, HCl, and QSO₄ in college-age smokers and nonsmokers. There were no consistent differences in thresholds for any compound between smokers and nonsmokers.     

Time course of recovery from gustatory adaptation to NaCl

Recovery from adaptation to NaCl was tested by comparing some relevant parameters of response to the adapting and test stimuli separated by different recovery intervals. The time course of response was determined using magnitude estimations and using the flow chamber for stimulus delivery. The course of recovery for all parameters used was a negatively accelerated function of the rest time, but the recovery rate of different parameters did not prove to be equal. Recovery was fastest for the initial maximum taste magnitude, followed by the time needed for the taste to disappear. The taste effect summed over time and the time required for the taste magnitude to decrease to 30% of its preadapted maximum were the slowest to recover. Although the recovery process proceeded at a rapid rate during the initial period, all parameters remained depressed over a rather long period.     

Time course of recovery from gustatory adaptation to NaCl.

Recovery from adaptation to NaCl was tested by comparing some relevant parameters of response to the adapting and test stimuli separated by different recovery intervals. The time course of response was determined using magnitude estimations and using the flow chamber for stimulus delivery. The course of recovery for all parameters used was a negatively accelerated function of the rest time, but the recovery rate of different parameters did not prove to be equal. Recovery was fastest for the initial maximum taste magnitude, followed by the time needed for the taste to disappear. The taste effect summed over time and the time required for the taste magnitude to decrease to 30% of its preadapted maximum were the slowest to recover. Although the recovery processes proceeded at a rapid rate during the initial period, all parameters remained depressed over a rather long period.     

Within-subjects positive and negative contrast effects in rats.

Rats were given alternating 1-min. access periods to 2 tubes containing either 32% or 4% sucrose solutions for daily 6-min. test sessions. Lick rate for 32% was higher under comparison (32 vs. 4) than noncomparison (32 vs. 32) conditions; and lick rate for 4% was lower under comparison conditions (4 vs. 32) than under noncomparison conditions (4 vs. 4). All sucrose conditions were varied within subjects and both positive and negative contrast were obtained with a small n. In addition to lick rate, intake and latency measures also revealed contrast effects. Deprivation conditions altered latency but not lick rate measures of contrast. Reducing the test session to 3 min. (alternating 30-sec. access periods) did not greatly affect contrast. Additional experiments provided evidence for distinct within-days and between-days contrast effects, as well as a between-groups contrast effect.     

Multiple fixed-interval schedules: transient contrast and temporal inhibition

Pigeons were exposed to four cycles per session of a multiple schedule in which each cycle involved twelve 60-sec fixed intervals followed by four 180-sec intervals [(12 FI 60-sec)(4 FI 180-sec) schedule]. Post-reinforcement pauses were shorter during the first few short intervals of each cycle than during later short intervals, and increased over the four long intervals of each cycle (positive and negative transient contrast). A (12 FI 15-sec)(4 FI 45-sec) schedule showed similar results. These two schedules differed in some other respects indicating effects of absolute FI duration on stimulus control. Differences in contrast properties between both these procedures and multiple variable-interval schedules were related to the pause-producing property of reinforcement on FI (temporal inhibition). Behavior under two other multiple fixed-interval schedules—(2 FI 360-sec)(1 FI 720-sec) and (3 FI 360-sec)(1 FI 720-sec)—differed in certain respects from both the (12 FI x-sec)(4 FI 3x-sec) schedules. These differences may be related to differences in the number of successive fixed intervals within a component (run length).     

Water taste in man

Taste quality and intensity shifts following adaptation to NaCl, quinine hydrochloride, sucrose and HCl were investigated in 10 Ss. In each of four sessions, Ss were adapted to water and two concentrations of one taste solution and gave magnitude estimates and quality judgments for a series of concentrations of that solution. Adapting to water produced magnitude estimates which increased with increasing concentration. Quality judgments were typical, e.g., “salty” for NaCl. Adapting to moderate concentrations of taste solutions generally produced magnitude estimates of zero at the adapting concentrations and increasing values for higher and lower (sub-adapting) concentrations. Sub-adapting tastes were atypical. Adaptation to NaCl and sucrose produced bitter sub-adapting tastes and adaptation to HCl and quinine hydrochloride produced sweet sub-adapting tastes. Water, as the lowest sub-adapting “concentration”, produced the largest sub-adapting tastes.     

Delayed matching in the capuchin monkey with brief sample durations

Two capuchin monkeys were trained in a delayed matching-to-sample task in which the duration that the sample was available for viewing was very brief, 0.075 to 0.45 sec. The matching performance of one animal was above chance with delay (retention) intervals as long as 4 min; the other S showed significant matching with a 2-min retention interval. The performance of both Ss was independent of sample exposure duration, indicating that their capacity to match successfully at long retention intervals is not dependent on repeated viewing of the sample stimulus. The marked practice effect shown by one S with prolonged training at 2-min delay suggests the capacity of “learning how to remember.” A constant high performance level on 2-sec delay control trials indicates that the observed practice effect was not the result of enhanced attending to the sample stimulus.     

Stimulus generalization and the response-reinforcement contingency

Generalization gradients along a line-tilt continuum were obtained from groups of pigeons that had been trained to peck a key on different schedules of reinforcement. In Exp. I, gradients following training on a differential-reinforcement-of-low-rate (DRL) schedule proved to be much flatter than gradients following the usual 1-min variable interval (VI) training. In Exp. II, the value of the VI schedule itself was parametrically studied; Ss trained on long VI schedules (e.g., 4-min) produced much flatter gradients than Ss trained on short VI schedules (30-sec; 1-min). The results were interpreted mainly in terms of the relative control exerted by internal, proprioceptive cues on the different reinforcement schedules. Several implications of the results for other problems in the field of stimulus generalization are discussed.     

Sex and menstrual cycle differences in the habituation and spontaneous recovery of the electrodermal orienting reaction

Sex and menstrual cycle differences have been widely observed in electrodermal activity. The aim of this study was to investigate these differences in the electrodermal orienting reaction employing a habituation-spontaneous recovery procedure. According to previous research it was predicted that men and preovulatory women should show higher electrodermal responses, higher skin conductance levels, and slower habituation rates. Thirty-two subjects (16 males and 16 females) were presented with two series of tones, 10 in the first series and eight in the second, with a 4-min rest period between the two series. Half of the subjects received the same 5-sec tone (80 dB, 1000 Hz) in each presentation while the other half received 80-dB, 5-sec tones which varied randomly in frequency (100, 500, 1000 Hz). Women were divided into two groups; preovulatory (n = 7) and postovulatory (n = 8) according to their answers to a retrospective questionnaire. The mean response amplitude was higher in the group of males, who habituated later than females. Postovulatory women showed lower orienting reactions in the first series, and habituated faster than did preovulatory women in the two series. There were neither significant differences between males and females, nor between preovulatory and postovulatory women in tonic conductance levels. These results support the existence of greater electrodermal reactivity in males and in preovulatory women.     

Primacy effect in orienting responses to auditory stimuli of tones and music.

This 25 factorial experiment investigated the primacy effect in the orienting response. The type of stimuli (tone or "music"), stimulus intensities (loud or soft), length of adaptation period (same, 5 or 30 sec; or different, 5 min.), interstimulus intervals (5 or 30 sec.), and sex were studied. College students, 32 males and 32 females were randomly assigned to each group. In the same condition, the tone (or music) was soft (or loud) for 5 sec. (or 30 sec.) in adaptation and was then changed alternately without interruption to loud, soft, etc. (or soft, loud, etc.) for 5 sec. (or 30 sec.). The different condition was identical except for the length of adaptation period in which the stimuli sounded continously for 5 min. Analyses of the GSR manifestation of the orienting responses indicated: (a) an over-all primacy effect with the auditory stimuli and (b) the primacy effect occurred in the 5-sec.-same but not in the 30-sec.-same condition as predicted.     

Effects of Number of Alternatives on the Psychological Refractoriness of an Extended Movement,

The single-channel prediction that delays in RT₂ should be proportional to RT₁ was examined by varying the number of alternatives (one, two, or three) in the primary response which was an extended arm swing at maximal speed. The second response was a thumb key release. Foreperiods were 2, 3, or 4 sec., and interstimulus intervals (ISIs) ranged from .10:50 sec. in .10-sec. steps. General support for the single-channel model was found in that RT₂ paralleled changes in RT₁. However, RT₂ was greater than predicted when the second signal (S₂) occurred during the execution of the primary response. In addition, while delays in RT₂ as a function of ISI – RT₁ showed corresponding differences between choice conditions, most values were greater than predicted. The deviations from the single-channel model appeared to be explained best in terms of a decrease in readiness to respond to the second signal as ISI lengthened.     

Effects of flavor salience on aversion performance following relatively long-delay backward conditioning procedures

Male albino rats (n = 144) received a 0.15 M injection of lithium chloride (at 2.0% body wt), followed 10, 30, or 75 min later by a 5.0% casein CS or a 10.0% sucrose CS, casein being the more salient CS. For each CS one-third of the rats received no fluid during the toxin-CS interval. The remaining two-thirds of the rats received 2-min access to distilled water or to a novel flavor 5 min after onset of the toxin-CS interval. For sucrose CS groups, the novel flavor was casein; for casein CS groups, the novel flavor was sucrose. Groups which received no fluid during the toxin-CS interval showed reliably greater aversion effects to the casein CS than to the sucrose CS. Results of Test Trial 1 showed that aversion to casein was relatively unchanged across toxin-CS intervals, while aversion to sucrose decreased reliably from the 10-min to the 30- and 75-min intervals. However, for each toxin-CS interval, aversion to the sucrose CS was reliably enhanced when casein access occurred in the interval, relative to that for distilled water or no fluid access. For the casein CS, access to sucrose or distilled water in the toxin-CS interval altered aversion effects, relative to the no fluid condition, depending on the interval.     

Reliability and Specificity of Individual Differences In Reminiscence

In investigating Eysenck’s (1965) suggestion of the specificity of reminiscence, 50 high school boys were tested on 2 gross motorcoordination tasks—one involving tracking and the other balance. In the practice schedule, which was identical for both tasks, all Ss were given 20 50-sec. trials with a 10-sec. intertrial rest. A 5-min. interpolated rest was given after every fourth trial. The reliability of individual differences in reminiscence for both tasks was found to be extremely low. While Eysenck’s hypothesis was not necessarily weakened, doubt was cast upon the specificity of reminiscence in the usual context of the word.     

The sensitivity of a palm-based psychomotor vigilance task to severe sleep loss

In this study, we evaluated the sensitivity of a 5-min personal digital assistant-psychomotor vigilance test (PDA-PVT) to severe sleep loss. Twenty-one participants completed a 10-min PVT-192 and a 5-min PDA-PVT at two hourly intervals during 62 h of sustained wakefulness. For both tasks, response speed and number of lapses (RTs > 500) per minute significantly increased with increasing hours of wakefulness. Overall, standardized response speed scores on the 5-min PDA-PVT closely tracked those of the PVT-192; however, the PDA-PVT was generally associated with more lapses/minute. Closer inspection of the data indicated that when the level of sleep loss and fatigue became more severe (i.e., Day 3), the 5-min PDA-PVT was not quite as sensitive as the 10-min PVT-192 when 2- to 10-sec foreperiods were used for both. It is likely, however, that the observed differences between the two devices was due to differences in task length. Thus, the findings provide further evidence of the validity of the 5-min PDA-PVT as a substitute for the 10-min PVT-192, particularly in circumstances in which a shorter test is required and/or the PVT-192 is not as practical.     

TEACHING CONVERSATION-RELATED SKILLS TO PREDELINQUENT GIRLS1

The use of conversation-related skills by youthful offenders can influence social interactions with adults. These behaviors are also likely to be useful to adolescents after their release from a treatment program (Journal of Applied Behavior Analysis, 1972, 5 , 343–372). Four girls, aged 13 to 15 yr, residing at Achievement Place for Girls in Lawrence, Kansas, received training on conversation-related behaviors. A multiple-baseline design across youths and across behaviors was used. Youth answer-volunteering in response to questions and three youth nonverbal components (“hand on face”, “hand at rest”, and “facial orientation”) were measured during daily 10-min sessions with a simulated guest in the group home's living room. Answer-volunteering was scored each session as the per cent of 13 “secondary” questions that the simulated guest did not have to ask following 10 “primary” questions. The three nonverbal components were scored according to their occurrence during 10-sec intervals and the resultant scores were averaged per session for an overall appropriate nonverbal score. The girls individually earned points within the home's token economy for participating in each session and additional points were awarded after training if preselected behavioral criteria were achieved for each of the two behavior categories per girl. Some of the training sessions were led by a “teaching-parent” (specially trained houseparent) while others were led by individual girls. Point consequences were administered by both the teaching-parent and by the “peer-trainers”. The average observed rate of answer-volunteering by the girls during pretraining sessions was 30% for S₁, 30% for S₂, 23% for S₃, and 68% for S₄. The average rate of answer-volunteering during posttraining sessions was: S₁ = 92%, S₂ = 89%, S₃ = 90%, and S₄ = 98%. The average nonverbal score during pretraining sessions was 82% for S₁, 53% for S₂, 60% for S₃, and 82% for S₄. The average nonverbal score during posttraining sessions was: S₁ = 98%, S₂ = 98%, S₃ = 98%, and S₄ = 100%. Videotapes of the sessions were shown in a random sequence to four adults (probation officer, social worker, etc who represented “significant others” for the youths' future success in the community. The adults judged posttraining tapes on the average as more appropriate 100% of the time for S₁, 100% of the time for S₂, 90% of the time for S₃, and 70% of the time for S₄. The study demonstrated that training of conversation-related skills is feasible with predelinquent girls, that the girls can help train each other, and that social validation of the training results is possible.     

Incomplete taste adaptation to different concentrations of salt and sugar solutions

Two concentrations each of sodium chloride and sucrose solutions were used as stimuli in a study examining taste adaptation. Twenty subjects were presented a 3-min continuous flow of each taste stimulus over the anterior dorsal tongue surface, and periodically gave magnitude estimates of its intensity. The degree of adaptation was greater for the less concentrated solutions than for the more concentrated ones, but the majority of subjects did not adapt completely to any of the stimuli. This result, which is consistent with other reports from this laboratory, is discussed in terms of individual differences among subjects and in relation to recent taste research based on completely adapted subjects.     

Asymmetry in updating long-term memory for time

The present study evaluates the updating of long-term memory for duration. After learning a temporal discrimination associating one lever with a standard duration (4 sec) and another lever with both a shorter (1-sec) and a longer (16-sec) duration, rats underwent a single session for learning a new standard duration. The temporal generalization gradient obtained 24 h later showed a modification in long-term memory for durations longer than the standard but only when the new duration was longer than the one initially learned. The effect was confirmed for another set of durations (0.5–2–8 sec). Our study demonstrates asymmetry in updating long-term memory for time.

Learning and memory updating are based on error detection, so that learning/updating occurs when something new happens. Time-based error detection supposes a comparison between current tracked time and stored/memorized time of the expected event. This is what is at work when on your usual way back home you are judging that the traffic light is broken because it has stayed red for too long, based on your memory of that traffic light duration.Memory of time has been invoked in early treatments of timing (Pavlov 1927; Treisman 1963; Gibbon 1977). Animal research has shown that long-term memory for time is formed in a single session, or even in a single trial (Balsam et al. 2010; Diaz-Mataix et al. 2013; Tallot et al. 2020), while human research has recently shown that it follows biological rules, such as a consolidation time course during the hours following encoding (Cocenas-Silva et al. 2014), which are different from those underlying temporary storage of duration. An in-depth investigation of the neural bases of long-term memory for time requires research in animals, in protocols that isolate the learning of duration from any other aspects of the task (e.g., contingencies and rules).One protocol is to shift temporal contingencies after the initial learning of the task has been stabilized in performance, and observe how updating occurs at the behavioral level. With this approach, human research has mainly concentrated on temporal reference memory created and manipulated within a single session, and thus has not studied its long-term form. For example, Ogden et al. (2008) reported interference in memory, as the temporal generalization gradient for a recently encoded duration was altered by the introduction of another generalization task, whether the new standard was of a shorter or longer duration. Also showing effects in both directions, Simen et al. (2011) found rapid adaptation to successive new, longer or shorter, time targets. Animal research has analyzed the dynamics of behavioral adaptation to new fixed interval (FI) values (e.g., Meck et al. 1984; Lejeune et al. 1997) or CS–US interval in a Pavlovian paradigm (Dallérac et al. 2017), changes in the duration–action association in temporal discrimination tasks (Church and Deluty 1977), or through the demonstration of averaging of time (FI) memories (e.g., Swanton et al. 2009; De Corte and Matell 2016). The difficulty with all these approaches is that they often necessitate several sessions to extract/analyze the behavioral outcome, while memory for the new time is presumably updated and consolidated within hours after the first session. In addition, the behavioral adaptation may differ depending on the magnitude and direction of the difference between the new relevant temporal values and those (shorter or longer) stored in long-term memory (Higa 1997; Lejeune et al. 1997). Importantly also is the fact that these approaches mix two factors: the learning of the new temporal rule and the behavioral adaptation to it, which likely depends on the behavioral protocol used, thus rendering interpretation of effects difficult to link with a specific factor. This may also explain in part why the results are conflicting with sometimes fast adaptation, or in contrast slow adaptation, or even no adaptation to new temporal rules.The aim of the present study was to assess in rats the ability to update in long-term memory a duration memorized in a single session. We developed a temporal generalization procedure, akin to human studies of memory for time (Cocenas-Silva et al. 2014; Derouet et al. 2019), enabling the use of both shorter or longer durations while isolating the formation of a new temporal memory through the investigation of the extent to which it interferes with an already formed stabilized memory. Rats were trained (temporal discrimination training) (see the Supplemental Material) to press one lever (left or right) after a 4-sec tone stimulus duration and the other lever after a shorter (1-sec) or longer (16-sec) tone duration, as an equivalent to the “same” versus “different” task in the training phase for temporal generalization assessment in humans (Wearden 1992). Reward (food pellet) was given if the correct lever was pressed. All the animals showed a good general level of acquisition and discrimination between the durations (see the Supplemental Material). Animals were then assigned to four groups, equilibrated according to their acquisition performance (Supplemental Fig. S1). For three groups, animals were submitted to a single session (called shift session) with 20 trials in which only one lever, the lever associated with the standard 4-sec duration, was presented at the end of the tone, but the tone duration was shorter than (2.5 sec), longer than (6.3 sec), or the same as (4.0 sec, no shift) the standard duration. Animals in the fourth group (control) remained in the colony room. Generalization tests were performed on the following 2 d, with six intermediate durations (2, 2.5, 3.2, 5, 6.3, 8 sec; 10 trials each) not reinforced, in addition to the standard duration (4 sec for 30 trials) and the two “extreme” durations (1 sec and 16 sec for 15 trials each) for which correct responding was reinforced.The generalization gradients obtained on the first day of tests, 24 h after the shift session, differed between groups, and more so for the durations longer than the standard (Fig. 1A). An analysis of variance (ANOVA) performed on the proportion of responses to the lever associated with the 4-sec standard duration, p(4 sec), with one between-subjects factor (four groups) and one within-subject factor (seven stimulus durations, excluding the reinforced extreme durations) showed a significant main effect of stimulus duration, F_(6,408) = 46.88, P < 0.001, confirming that rats did effectively discriminate between durations. However, there was a significant stimulus duration × group interaction, F_(18,408) = 1.892, P = 0.046, while the main effect of group was not significant F_(3,68) < 1. This indicated that rats responded differently among groups depending on the durations. Parsing the interaction, separate analyses, with stimulus durations shorter (2, 2.5, 3.2 sec) and longer (5, 6.3, 8 sec) than the standard (4-sec) duration, revealed a significant stimulus duration × group interaction for long stimulus durations, F_(6,136) = 4.050, P = 0.001, but not for short-stimulus durations, F_(6,136) = 1.494, P = 0.188. Thus, the impact of the Shift session was specifically on stimulus durations longer than the standard duration. To characterize the effect, further comparisons were made restricted to these long stimulus durations. First, the 4-sec group did not differ significantly from the control group (no significant interaction or group differences, both Fs < 1). This demonstrated that the procedure itself (i.e., a forced-choice session with a single “standard” duration) did not produce a change in temporal generalization gradient. Second, compared with the 4-sec group, only the group of animals that experienced a shift session with a new standard >4 sec showed a significantly modified generalization gradient (6.3-sec group: interaction, F_(2,68) = 5.236, P = 0.010, group effect, F_(1,34) < 1); 2.5-sec group: interaction, F_(2,68) = 1.501, P = 0.232, group effect, F_(1,34) = 1.662, P = 0.206). Analysis of individual slopes of regression confirmed that the decay magnitude of the generalization gradient differed among groups, F_(3,68) = 6.38, P < 0.001, and that only the 6.3-sec group differed from all the other groups, that is, the control group (Bonferroni, P = 0.035), the 4-sec group (P = 0.05), and the 2.5-sec group (P < 0.001) (Fig. 1A, inset). None of the other comparison pairs was significant (Ps ≥ 0.738) (see Supplemental Fig. S2 for individual curves and slopes of regression for the rising and decay parts of the generalization gradient). Thus, the shift session with a new temporal reference had a significant impact only when it was to a longer duration than the initially learned standard duration, and the impact was asymmetrical with a flattening of the generalization gradient only for the stimulus durations longer than the standard duration.Open in a separate windowFigure 1.Proportion of lever presses on the 4-sec lever -p(4 sec)- plotted against stimulus duration for the control, 4-, 2.5-, and 6.3-sec groups for the first (A) and the second (B) day of the generalization task. Error bars: ±SEM. (Insets) Slope of the regression fitted on p(4 sec) for 5-, 6.3-, and 8-sec test durations for each rat for the four groups, with a dotted line linking the group mean values. (*) Bonferroni P ≤ 0.05, significant difference between the 6.3-sec group and each of the other groups.As the original discrimination rules were in effect during the generalization test (i.e., retraining with the standard [4-sec] and extreme durations reinforced), the impact of the shift session should diminish with retraining. As expected, apart from the main effect of stimulus duration, F_(6,408) = 84.261, P < 0.001, showing that the rats still discriminated among durations, there were no other significant effects during the second day of the generalization test (effect of group and stimulus duration × group interaction, both Fs < 1, ns) (Fig. 1B). Thus, the disruption of temporal judgment observed in the generalization test originated from the interference effects of the new temporal rule in the shift session, and reflected a rapid update in memory of the duration/action association rather than a general irreversible disturbance of behavior.The asymmetry in the temporal generalization gradient suggesting interference effects only on the judgment of stimulus durations longer than the standard duration raises the question of whether it reflects an effect specific to the range of durations used in our study, with judgment of durations <4 sec being immune to interference. It is also possible that memory updating requires a minimum temporal difference from the standard duration (2.3 sec vs. 1.5 sec, for shifts to longer and shorter durations, respectively). To address this issue, a new set of animals was trained on a discrimination between a 2-sec tone standard duration associated with a given lever, and either a 500-msec or 8-sec tone duration associated with the second lever (see the Supplemental Material). A shift session with a 3.15-sec tone duration (i.e., 1.15-sec difference from the standard) was given for one group compared with another group for which the 2-sec standard duration was not changed. The performance criterion was reached by both groups for the standard and long duration, but not for the 500-msec tone (see the Supplemental Material; Supplemental Fig. S3). Performance during the first day of the generalization test (1.25, 1.60, 2.5, 3.15 intermediate durations) run 24 h after the shift session showed an impact of the shift session when the new 3.15-sec duration was associated with the lever corresponding to the 2-sec standard duration, compared with when there was no change in duration (Fig. 2A). The mixed ANOVA performed on p(2 sec) confirmed that rats discriminated between durations (main effect of stimulus duration, F_(6,210) = 12.212, P < 0.001), with no significant main effect of group, F_(1,35) < 1, but a significant stimulus duration × group interaction, F_(6,210) = 3.483, P = 0.008), indicating that rats responded differently between groups depending on the stimulus durations. As in the previous experiment, a significant stimulus duration × group interaction appeared for stimulus durations longer (2.5, 3.15, 4 sec), F_(2,70) = 7.612, P = 0.001, but not for those shorter (1, 1.25, 1.60 sec) than the standard duration (F < 1). Analysis of individual slopes of regression confirmed a significant difference between the two groups for the decay part of the generalization gradient (F_(1,35) = 9.65, P = 0.004) (Fig. 2A, inset; see Supplemental Fig. S4 for individual curves and slopes of regression for the rising and decay parts of the generalization gradient). Also as before, the effect was no longer visible on the second day of generalization test (F < 1 for group effect and stimulus duration × group interaction) (Fig. 2B) while the main effect of stimulus duration remained significant, F_(6,210) = 14.580, P < 0.001). Thus, a 1.15-sec shift in the duration/action association within a range of durations <4 sec triggered an update in memory with an impact restricted specifically to durations longer than the standard duration. This effect was comparable with the one observed when the standard duration was 4 sec in duration and the memory update was to a longer duration with the same magnitude on a geometric scale (factor 1.575).Open in a separate windowFigure 2.Proportion of lever presses on the 2-sec lever -p(2 sec)- plotted against stimulus duration for the 2-sec and 3.15-sec groups for the first (A) and the second (B) day of generalization task. Error bars: ±SEM. (Insets) Slope of the regression fitted on p(2 sec) for 2.5-, 3.15-, and 4-sec test durations for each rat for the two groups, with a dotted line linking the group mean values. (*) Bonferroni P ≤ .05, significant difference between the 3.15-sec group and the 2-sec group.In all, the results show that a single session pairing a new duration with a learned response interferes with an already formed long-term memory of a duration–action association. This result first provides further support for rapid learning of duration, extending the previous findings in Pavlovian settings in which a single trial was shown to suffice for learning an interval between conditioned and unconditioned stimuli (Balsam et al. 2010; Diaz-Mataix et al. 2013). In instrumental tasks, only few studies have examined the time course of behavioral adaptation, and the majority of them used paradigms in which the animals were repeatedly exposed to shifts in fixed interval values, and therefore may have learned to adapt. Nevertheless, when analyzed, the behavioral shifts were rapid, if not in a single trial (e.g., Higa et al. 2002).The procedure we implemented here enabled us to highlight two, possibly independent, sources of asymmetry: (1) Memory updating was produced when the new standard duration was longer (upshift), but not shorter (downshift), than the initially trained standard duration. (2) The impact of the interference on the generalization gradient (i.e., flattening of the curve) was restricted to durations longer than the standard. The asymmetry cannot be due to a differential detection of temporal changes, as their sizes were equivalent on a geometric scale (in all upshift and downshift conditions), or even opposite to the effect predicted when comparing the two experiments on an arithmetic/absolute scale (significant impact of a 1.15-sec upshift in experiment 2 vs. no impact of a bigger 1.5-sec downshift in experiment 1). These asymmetrical effects resonate with previous reports showing asymmetries in the adaptation to new fixed interval values or to new duration/action association, albeit not always in the same direction. Shifts in fixed or peak interval schedules in rodents have produced mixed results, with reports of either symmetry or a tendency for faster adaptation to longer durations (e.g., Meck et al. 1984; Lejeune et al. 1997) or, in contrast, slower, or in some instances, no adaptation to the new schedule when the shift was to a longer duration, but faster adaptation when the shift was to a shorter duration (e.g., Higa 1996; 1997; Higa and Tillou 2001). Furthermore, readaptation to a short duration after a shift to longer duration is very rapid (Higa and Tillou 2001), which stands in contrast to our results, which could be interpreted as a fast learning of a longer duration and/or slow readaptation to a shorter duration. Previously reported asymmetries in adaptation to changing FI schedules may be partly explained through the learned anticipation of upcoming shifts, due to the repetition of shifts (Sanabria and Oldenburg 2014).Our results may be better compared with tasks involving choice rather than anticipatory responding. In the temporal bisection task, no asymmetry has been reported in rats after shift to new duration/action pairings, whether to shorter or longer ranges (Church and Deluty 1977), but some asymmetry has been reported in pigeons with a noticeable change in behavior mainly when the long anchor duration was lengthened (Machado and Keen 2003), whose magnitude may depend on the initial training condition (Araiba and Brown 2017). In this type of task, categorization processes may be at play in addition to temporal generalization, possibly rendering the behavior less sensitive to changes in duration. However, the present observed asymmetry would suggest that the short and standard durations may have belonged to the same category, which is opposite to findings in the literature (Russell and Kirkpatrick 2007). Although our paradigm involved a discrimination task similar to the same/different task and temporal generalization gradient test used in humans, it can also be regarded as a discrimination with three—short versus standard versus long—durations, and a “dual”-bisection task during tests with intermediate duration values. The standard duration in our paradigm could be considered as a “long” anchor for the short–standard discrimination, but as a “short” anchor for the standard–long discrimination. In the first case, larger changes in behavior would be expected in the upshift condition than in the downshift condition (Araiba and Brown 2017), whereas in the second case no change would be expected (Machado and Keen 2003). Our results seem congruent with the reported asymmetry in the first case, and may also explain the lack of modification in the temporal generalization for the range of durations shorter than the standard duration.By restricting the change in duration/action association to a single session of interference, rather than looking at repetitive or stable adaptation of behavior to new temporal contingencies, our experiment reveals new information about how a duration is learned and memorized in long-term memory, to serve as a reference for later comparison when choices are made. We show that memory updating happens rapidly and the new temporal reference is memorized for long-term storage for at least 24 h. Our results, however, clearly point to an asymmetry in updating the memory, an asymmetry that was also suggested in our recent experiment in humans (Derouet et al. 2019). Whether the asymmetry originates from an asymmetrical detection of changes, that is, shorter versus longer than the standard duration, or from differential speed of learning and/or adaptation to temporal contingencies will need to be addressed in future investigations. The present novel paradigm will enable answering these questions and provide grounds for fruitful assessments of the neurobiological basis of memory for time, critical for time-based error monitoring and adaptation of behavior to novel contingencies.     

Conditioned reinforcement in second-order schedules

Pigeons responded under a schedule in which food was presented only after a fixed number of fixed-interval components were completed. Two such second-order schedules were studied: under one, 30 consecutive 2-min fixed-interval components were required; under the other, 15 consecutive 4-min fixed-interval components were required. Under both schedules, when a 0.7-sec stimulus light was presented at completion of each fixed interval, positively accelerated responding developed in each component. When no stimulus change occurred at completion of each fixed interval, relatively low and constant rates of responding prevailed in each component; a similar result was obtained when a 0.7-sec stimulus change occurred at completion of each fixed interval except the one which terminated with primary reinforcement. The 0.7-sec stimulus correlated with food delivery was an effective conditioned reinforcer in maintaining patterns of responding in fixed-interval components despite low average frequencies of food reinforcement.