Interference processes in monkey auditory list memory

A rhesus monkey’s memory was tested for single items and four-item lists of natural and environmental sounds. Memory items were presented from a center speaker, followed by a retention delay and then a choice response to a test sound presented simultaneously from two side speakers. Recognition of the last item of four-item lists was much poorer than that of single items at 0-, 1-, and 2-sec delays, despite there being the same temporal relations between study and test. This result showed that the first three items proactively interfered with memory of the last list item. Proactive interference dissipated after 2 sec, revealing a recency effect that eventually equaled single-item performance. Recognition of the first item of four-item lists was much poorer than single items at 20- and 30-sec delays, showing that the last three items retroactively interfered with memory of the first list item. The results point to the critical nature of interference processes in the understanding of serial position functions.     

Monkey auditory list memory: tests with mixed and blocked retention delays

A rhesus monkey was tested in an auditory list memory task with blocked and mixed retention delays. Each list of four natural or environmental sounds (from a center speaker) was followed by a retention delay (0, 1, 2, 10, 20, or 30 sec) and then by a recognition test (from two side speakers). The monkey had been tested for 12 years in tasks with blocked delays. An earlier (4 years prior) blocked-delay test was repeated, with virtually identical results. The results from the mixed-delay test were likewise similar. Thus, the peculiarities of blocked-delay testing, such as delay predictability or differences in list spacing, apparently do not alter this monkey's memory for auditory lists. It is concluded from this and other evidence that the monkey's serial position functions reflect mnemonic processes that change with changes in retention delay and are not artifacts of the blocked-delay procedure. The nature of the monkey's auditory memory is discussed.     

Delayed matching in the pigeon: Effect on performance of sample-specific observing responses and differential delay behavior

Pigeons were trained on a delayed matching-to-sample task with a 0-sec delay and then transferred to a 1-sec delay (Experiment 1) or were trained with mixed 0-sec/1-sec delays and then transferred to longer mixed delays up to 28 sec (Experiment 2). Four groups were distinguished by the nature of the observing response required to each sample color (red and blue). For Group NN pecks were allowed to neither color. For Group PcPc pecks were required to both colors. For Group PcN pecks were required to red but were not allowed to blue. For Group PcPt pecks were required at the center key in the presence of red, but at a key located directly above the center key in the presence of blue. The results of both experiments indicated significant effects of both Pecking vs Not Pecking, and Sample-Specific vs Sample-Independent Responding. At the longer delays individual differences in sample-specific delay behavior were a better predictor of performance than the behavior required in the presence of the sample.     

Control of pigeons' matching-to-sample performance by differential sample response requirements

Pigeons were trained on a matching-to-sample task in which sample hue and required sample-specific observing behavior provided redundant, relevant cues for correct choices. On trials that involved red and yellow hues as comparison stimuli, a fixed-ratio 16 schedule (FR 16) was required to illuminate the comparisons when the sample was red, and a differential-reinforcement-of-low-rates 3-sec schedule (DRL 3-sec) was required when the sample was yellow. On trials involving blue and green hues as comparison stimuli, an FR 16 schedule was required when the sample was blue and a DRL 3-sec schedule was required when the sample was green. For some pigeons, a 0-sec delay intervened between sample offset and comparison onset, whereas other pigeons experienced a random mixture of 0-sec and 2-sec delay trials. Test trial performance at 0-sec delay indicated that sample-specific behavior controlled choice performance considerably more than sample hue did. Test performance was independent of whether original training involved all 0-sec delay trials or a mixture of 0-sec and 2-sec delays. Sample-specific observing response requirements appear to facilitate pigeons' matching-to-sample performance by strengthening associations between the observing response and correct choice.     

Spontaneous private speech and performance on a delayed match-to-sample task

Spontaneous private speech samples were obtained from 65 kindergarten children (mean age 70.3 months) from one suburban (n = 36) and one city (n = 29) school as they worked alone on a delayed match-to-sample (DMS) task with three levels of difficulty (2, 10, and 30 sec delays). As expected increases in DMS delay intervals produced decreased performance and increases in private speech. The expected increased positive relationship between task relevant private speech and performance for longer delays was found in city children but not suburban children. Since mean IQ scores were significantly different for the two groups this variable was further examined in post hoc analyses and discussed along with socio-economic status as possible explanations for the observed school-sample differences. A within-subject comparison for all children showed the percentage of speaking trials correct at 30-sec delay to be significantly greater than the percentage of nonspeaking trials correct. The effect of one experimenter modeled trial on a subsequent 10 trials at 30-sec delay was to increase speech and performance and to show a stronger relationship between speech and performance than for premodeling trials. These exploratory findings with a relatively simple two color matching task suggest further explorations of spontaneous private speech as a way of studying internalization of self regulatory cognitive strategies.     

Effect of delay-interval illumination on matching behavior in the capuchin monkey

Experiment 1 demonstrated that delayed matching-to-sample in the capuchin monkey was superior when the delay interval was spent in darkness rather than in moderate illumination. In contrast with previous studies in which the delayed-matching ability of primates appeared limited to 60 sec or less, in the dark condition all subjects showed above-chance matching at a 120-sec delay interval. Experiment 2 verified that darkness during the delay interval can facilitate delayed matching and provided evidence that the effective variable was the illumination level of the delay interval rather than change in illumination, which in Exp. 1 was confounded with illumination level.     

Conditioned suppression and conditioned enhancement with the same positive UCS: an effect of CS duration

Previous experiments have shown that positively reinforced operant responding is suppressed during a conditioned stimulus terminated with an electric shock (conditioned suppression). In the present experiment, the conditioned stimulus was terminated with a positive unconditioned stimulus, and it was found that the duration of the conditioned stimulus was a key factor in determining whether response suppression or response enhancement was observed during the stimulus. The lever-pressing responses of rats were maintained by a variable-interval schedule of food reinforcement. While the rats were pressing the lever, a light was occasionally turned on, its offset coincident with a brief period of access to a sucrose solution. In consecutive blocks of sessions, the light duration was 40 sec, 12 sec, or 120 sec. Results showed that the rate of lever pressing was substantially suppressed during the 12-sec stimulus, slightly suppressed during the 40-sec stimulus, and enhanced during the 120-sec stimulus.     

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.     

Choice behavior and the accessibility of the reinforcer

In Experiment 1, matching of relative response rates to relative rates of reinforcement was obtained in concurrent variable-interval schedules when the absolute values of the two concurrent variable-interval schedules varied from 6 sec and 12 sec to 600 sec and 1200 sec. Increases in the duration of the changeover delay, however, produced decreases in the relative response rates and, consequently, some deviation from matching. In Experiment 2, matching of relative response rates to the relative duration of the reinforcer failed to occur when the equal variable-interval schedules arranging access to the two different reinforcer durations (1.5 and 6 sec) were varied in size from concurrent variable-interval 10-sec schedules to concurrent variable-interval 600-sec schedules.     

Pigeons may not remember the stimuli that reinforced their recent behavior

In two experiments the conditioned reinforcing and delayed discriminative stimulus functions of stimuli that signal delays to reinforcement were studied. Pigeons' pecks to a center key produced delayed-matching-to-sample trials according to a variable-interval 60-s (or 30-s in 1 pigeon) schedule (Experiment 1) or a multiple variable-interval 20-s variable-interval 120-s schedule (Experiment 2). The trials consisted of a 2-s illumination of one of two sample key colors followed by delays ranging across phases from 0.1 to 27.0 s followed in turn by the presentation of matching and nonmatching comparison stimuli on the side keys. Pecks to the key color that matched the sample were reinforced with 4-s access to grain. Under some conditions of Experiment 1, pecks to nonmatching comparison stimuli produced a 4-s blackout and the start of the next interval. Under other conditions of Experiment 1 and each condition of Experiment 2, pecks to nonmatching stimuli had no effect and trials ended only when pigeons pecked the other, matching stimulus and received food. The functions relating pretrial response rates to delays differed markedly from those relating matching-to-sample accuracy to delays. Specifically, response rates remained relatively high until the longest delays (15.0 to 27.0 s) were arranged, at which point they fell to low levels. Matching accuracy was high at short delays, but fell to chance at delays between 3.0 and 9.0 s. In Experiment 2, both matching accuracy and response rates remained high over a wider range of delays in the variable-interval 120-s component relative to the variable-interval 20-s component. The difference in matching accuracy between the components was not due to an increased tendency in the variable-interval 20-s component toward proactive interference following short intervals. Thus, under these experimental conditions the conditioned reinforcing and the delayed discriminative functions of the sample stimulus depended on the same variables (delay and variable-interval value), but were nevertheless dissociated.     

The influence of the acoustic context on vertical sound localization in the median plane

The influence of background sounds (frames) on vertical localization of single sound sources (targets) was examined in four experiments. Loudspeakers (five targets and four frames) were positioned in the median plane, ranging from +30 degrees to -30 degrees above and below the subject's ear level. The subjects determined the vertical position of the targets by either verbal judgments or manual pointing. Frame and target sounds were presented concurrently or successively with a 1-sec interval; both consisted of (1) 300-Hz square waves, (2) noise, or (3) targets of noise and frames of 300-Hz square waves. Particularly in the second condition, the subjects consistently shifted the apparent target positions away from the frame locations. This contrast effect persisted even 1 sec after the offset of the frames. No effect was found with different waveforms for the frame and the target. Results are related to recent findings indicating a similar effect in the azimuthal dimension. Possibly the effect is based on a mechanism in which the auditory system adapts to recently heard sound source positions.     

Delayed discrimination and delayed matching in pigeons

Three pigeons were each trained to perform a discrimination problem and a matching problem. Following acquisition, delays of 1 to 7 sec were interposed after stimulus presentation on both problems. Accuracy of responding on these two types of delay procedures was observed to be a function of length of delay interval. Performance was consistently poorer on the delayed matching problem than on the delayed discrimination problem.     

Delay of gratification in children: The effects of training under fixed,decreasing and increasing delay of reward

The effect of fixed, gradually decreasing, or increasing delay of reward in discimination learning on later delay of gratification was investigated. In discrimination training, employing a correction procedure, a candy reward was delivered either after 0, 10, 20, 40 or 60 sec fixed delay; or after 60 sec in the first block of trials and decreased in successive block; or reward was immediate in the first block of trials and delay was gradually increased to 60 sec. In the delay of gratification tests, subjects could press a button immediately to receive a small reward (one candy or a cheap toy) or delay pressing and receive an increasingly larger reward (more candy or a better toy).Learning was not significantly affected by either fixed or decreasing delays. Increasing delays resulted in faster learning than decreasing delays. The increasing delay group demonstrated superior delay of gratification on both tests. Fixed delay groups did not differ significantly among themselves, nor from the decreasing delay group. The effectiveness of exposure to increasing delays in facilitating delay of gratification was interpreted as due to either the acquisition of coping responses or the extinction of frustration.     

Motion aftereffects with horizontally moving sound sources in the free field

A horizontally moving sound was presented to an observer seated in the center of an anechoic chamber. The sound, either a 500-Hz low-pass noise or a 6300-Hz high-pass noise, repeatedly traversed a semicircular arc in the observer's front hemifield at ear level (distance: 1.5 m). At 10-sec intervals this adaptor was interrupted, and a 750-msec moving probe (a 500-Hz low-pass noise) was presented from a horizontal arc 1.6 m in front of the observer. During a run, the adaptor was presented at a constant velocity (-200 degrees to +200 degrees/sec), while probes with velocities varying from -10 degrees to +10 degrees/sec were presented in a random order. Observers judged the direction of motion (left or right) of each probe. As in the case of stimuli presented over headphones (Grantham & Wightman, 1979), an auditory motion aftereffect (MAE) occurred: subjects responded "left" to probes more often when the adaptor moved right than when it moved left. When the adaptor and probe were spectrally the same, the MAE was greater than when they were from different spectral regions; the magnitude of this difference depended on adaptor speed and was subject-dependent. It is proposed that there are two components underlying the auditory MAE: (1) a generalized bias to respond that probes move in the direction opposite to that of the adaptor, independent of their spectra; and (2) a loss of sensitivity to the velocity of moving sounds after prolonged exposure to moving sounds having the same spectral content.     

Auditory spatial responses of young guinea pigs (Cavia porcellus) during and after ear blocking

Newborn guinea pigs were tested to determine their ability to approach an auditory stimulus early in development. Observations of the behavior of 1-4-day-old animals in a circular eight-choice maze revealed a pronounced tendency to orient toward and approach a tape-recorded signal of guinea pig vocalizations. The occurrence of approach responses was reduced to chance in animals tested with one ear occluded by wax ear plugs which attenuated but did not totally eliminate sound. The effect of monaural ear blocks was more severe than binaural blocks, which reflects the importance of binaural cues in the maintenance of approach responses to sound. In a second study, the ability of older animals, 11-31 days of age, was examined. Directional approach responses to sound were also evident at this age, and ear plugs disrupted performance only under monaural conditions. Furthermore, in animals raised from birth with monaural ear blocks but tested without ear plugs, there was a subsequent disruption of performance for at least 21 days. These results indicate the importance of binaural cues in the development of early auditory spatial responses and suggest the need for appropriate binaural experience for subsequent localization of sounds.     

Short-term memory and information processing in pigeons

Six pigeons were trained to asymptotic performance on a variable-delay matching-to-sample task in which the samples were sometimes line or color elements and sometimes line-color compounds. On compound-sample trials, the comparison stimuli were sometimes color elements and sometimes line-tilts. Sample type and delay (0, 1.5, and 4.5 sec) were varied within sessions, and sample duration (.4, 1.0, and 3.0 sec) was varied between sessions. Forgetting curves were steeper for line-tilt than for color. As sample duration increased, matching performance improved more for colors than for line-tilts, especially at delays greater than zero. Performance was better with element samples than with compound samples only on the line-tilt dimension at zero delay. Some predictions of a unitary trace growth and decay theory of pigeon short-term memory were not confirmed. A dual-code hypothesis was proposed to account for the data.     

Time decay of auditory stream biasing

In an experiment designed to investigate the time decay of auditory stream biasing (ASB), subjects were required to listen to a 10-sec induction sequence of repeated tones (AAAA …) designed to bias the listener’s percept toward hearing an A stream. The induction sequence was followed immediately by a silent interval (0–8 sec), and then a short ABAB … test sequence. To measure the amount of ASB remaining at the end of the silent interval, subjects were asked to indicate whether the test sequence was temporally coherent or had segregated into separate A and B streams. A plot of the mean number of segregation responses against silent-interval duration indicated that the overall time decay of ASB can be described by an exponential decay function with a time constant of t = 3.84 sec, with musicians having a longer time constant (τ = 7.84 sec) than nonmusicians (τ = 1.42 sec). The length of the time constants for musicians and nonmusicians suggests that the mechanism responsible for ASB is associated with long auditory storage and that future experiments investigating auditory streaming phenomena should use interstimulus intervals of at least 8 sec.     

Temporal contiguity and the judgement of causality by human subjects

Three experiments examined the role of the degree of temporal contiguity between an action and an outcome in human causality judgement. In all the experiments subjects were required to perform an action—pressing a key on a computer keyboard—and to judge the extent to which the action caused an outcome on the computer screen to occur. The action and outcome occurred on a free-operant schedule. In the first experiment a 2-sec delay between the action and outcome reduced causality judgements relative to a situation in which there was no delay. In the second experiment judgements in conditions with delays of 0, 4, 8, and 16 sec were compared with judgements in conditions in which the same pattern of outcomes occurred non-contingently with respect to the subjects' responding. In both of these experiments the events were controlled by random ratio schedules, following the procedure of Wasserman, Chatlosh, and Neunaber (1983), in which each condition was divided into 1-sec intervals. In the third experiment judgements in conditions with delays of 0, 2, 4, or 8 sec were compared in a continuous procedure rather than one divided into 1-sec intervals. In all experiments the increasing delays led to progressively lower judgements of causality. The results are related to three accounts of the mechanism underlying human causality judgement and are also compared with results from analogous animal conditioning studies.     

Directed forgetting of elements in compound samples.

Pigeons were trained in a delayed matching-to-sample procedure in which the sample stimuli consisted of a compound of color (red or green) and spatial location (left or right). A postsample cue (houselight on or off) signaled whether color matching or location matching would be required following the delay. In Experiment 1, the reduction in performance on probe trials (in which the houselight condition was reversed relative to that on regular trials) was greater for location matching than for color matching. The birds showed overt mediational behavior during the delays on location-matching trials. On color-matching trials, the birds exhibited behavior during delays that might have interfered with that mediational behavior. In Experiment 2, the houselight condition was changed shortly before presentation of the comparison stimuli on probe trials. Accuracy of location matching was reduced when the cue initially signaled color matching and was then changed to signal location matching, whereas matching accuracy was not reduced by a change in the opposite direction. Accuracy of color matching was reduced by a change in illumination level from dark to light, regardless of type of the relevant dimension signaled by houselight illumination. Discussion of these findings focuses on the variables critical to establishment of an effective cue to forget.     

Acquisition of delayed matching in the pigeon

Pigeons were exposed to three successive matching-to-sample procedures. On a given trial, the sample (red, green or blue light) appeared on a center key; observing responses to this key produced the comparison stimuli on two side keys. Seven different experimental conditions could govern the temporal relations between the sample and comparison stimuli. In the "simultaneous" condition, the center key response was followed immediately by illumination of the side key comparison stimuli, with the center key remaining on. In "zero delay" the center key response simultaneously turned the side keys on and the center key off, while in the "variable delay" conditions, intervals of 1, 2, 4, 10, and 24 sec were interposed between the offset of the sample and the appearance of the comparison stimuli on the side keys. In all conditions, a response to the side key of matching hue produced reinforcement, while a response to the non-matching side key was followed by a blackout. In procedure I all seven experimental conditions were presented in randomly permutated order. After nine sessions of exposure (at 191 trials per session, for a total of 1719 trials) the birds gave no evidence of acquisition in any of the conditions. They were therefore transferred to Procedure II, which required them to match only in the "simultaneous" condition, with both the sample and comparison stimuli present at the same time. With the exception of one bird, all subjects acquired this performance to near 100% levels. Next, in Procedure III, they were once more exposed to presentation of all seven experimental conditions in random order. In contrast to Procedure I, they now acquired the delay performance, and were able to match effectively at delays of about 4 sec.