Infant responses of ocular fixation to moving visual stimuli

Infants of 1, 2, and 3 months of age were presented with two checkerboard patterns, one stationary and the other moving in a horizontal oscillatory motion at one of eight rates. An observer who could see only the infant's head and eyes recorded, for each 30-sec trial, (a) the position of first fixation, (b) position of fixation at the end of each 5-sec interval, and (c) a final forced-choice judgment of the position of the moving stimulus. Results showed reliable differences in ocular behavior as a function of rate of stimulus motion for all three groups of infants.     

Women's verbal estimation of a 40-second interval during the first week postpartum: a replication.

In this replication research 49 mothers verbally estimated a 40-sec. interval each day for the first seven days after delivery. Throughout this postpartum period mothers overestimated the time interval. Findings of this study confirmed the results of the original 1987 research.     

Activation of Locations in Working Memory in Cats

Cats saw an object appear and disappear at two successive locations; the movement of the object from one location to the other was not perceived but was indicated by indirect cues and the two disappearances were separated by a 0-sec or a 20-sec interval. Performance was poorer with the 0-sec than with the 20-sec interval. With the 0-sec interval, the percentages of search attempts made at the object's initial and final hiding locations did not differ whereas with the 20-sec interval, more search attempts were made at the final than at the initial location. These results provide additional support to Goulet, Dore and Rousseau's (1994) interpretation of cats' search behaviour in terms of activation of spatial locations in working memory.     

Associative competition in operant conditioning: blocking the response-reinforcer association

Naive rats were trained to leverpress with a 30-sec delay-of-reinforcement contingency from the start of training. In Experiment 1, the delay interval for different groups of subjects included a signal in the first 5 sec, a signal in the last 5 sec, or no signal at any time. Rats with the signal at the start of the delay interval learned most rapidly. Rats with the signal at the end of the delay failed to learn. In Experiment 2, a choice procedure was used, in which each of two levers was associated with its own 30-sec delay of reinforcement. The delay for one lever included a 5-sec signal at the end of the delay. The delay for the second lever had no signal in its 30-sec delay. Preference was in favor of the lever without the signal in the delay interval. The results demonstrate that the acquisition of new response can be blocked in a manner analogous to the blocking of Pavlovian conditioning.     

Varying temporal placement of an added stimulus in a fixed-interval schedule

One paradigm for exploring stimulus effects on behavior is defined for steady state experiments. The paradigm is illustrated by a 60-sec fixed-interval reinforcement schedule wherein a 6-sec light is introduced into each interval. The temporal relation of this stimulus to the reinforcer is the independent variable that is systematically explored. Two experiments studied this temporal relation under two parametric conditions: (a) when the 6-sec light occurs once in each 60-sec interval, (b) when the 6-sec light occurs twice in each interval, the second time always during the 6 sec immediately preceding the reinforcer. Functions are presented showing the effect of the 6-sec light on responding at all points in the fixed-interval.     

Stimulus conditions affecting rate of acquisition in a computer-operated version of the two-way active avoidance procedure

Several experiments were performed with rats in order to investigate the stimulus conditions affecting the rate of acquisition of two-way active avoidance. The number of trials per session, the duration of the Conditioned Stimulus (CS), the intertrial interval (pause time), and the intensity of the shock presentation were each varied in separate experiments. The optimal, yet practicable, conditions required to obtain a fast rate of acquisition included 40 to 60 trials per session, a 40-sec intertrial interval, a 10-sec Conditioned Stimulus presentation and a shock intensity of 1.0 mA. These results are discussed with regard to the problem of standardization in behavioral research manipulating biological independent variables.     

The development of alertness

Two experiments explored variation in the alerting process across age and warning interval as well as the effects of alertness on subsequent processing. Experiment 1 obtained alertness functions for a group of 5-year-olds, 8-year-olds, and adults. Results revealed strong age differences in speed of alerting and in maintenance of alertness over a 1-sec interval. Five-year-olds alerted more slowly than older groups and sustained optimal alertness less well. Both groups of children showed more variability in alerting functions compared with adults. Experiment 2 examined the degree to which age differences in processing speed were attributable to differential speed and maintenance of alerting. Masking functions obtained across variations in the alerting interval revealed that when level of alertness was optimal in both 5-year-olds and adults, minimal age differences in processing speed were observed. During short, nonoptimal alerting intervals, speed of processing in adults was faster than in 5-year-old children. The pattern of results across studies suggested that alertness can fluctuate over time in young children, that level of alertness affects subsequent perceptual processing speed, and that developmental variation in speed and maintenance of alertness can partly explain observed age differences in processing speed. The potential role of alertness in more complex cognitive tasks is discussed.     

Heart rate conditioning in young infants using a visual conditional stimulus

Trace heart rate conditioning was evaluated in 16 infants having a mean age of 4.5 months. The Experimental Group received a 3-sec blinking light pattern as the CS, followed by a 3-sec interstimulus interval (ISI), and 3-sec tone as the UCS. The Control Group received an equal number of presentations of the CS and UCS at randomized intervals and in a randomized order. The acquisition of a conditioned deceleration during the period which included the visual CS and the ISI was demonstrated only in the Experimental males. Response differences were also found in the absence of the auditory UCS, with only Experimental females exhibiting a deceleration.     

The role of autopecking in behavioral contrast

Four groups of four pigeons each were studied on two different multiple schedules. The cues correlated with the schedule components were localized on the response key for two groups and were not localized for the others. Two groups worked on multiple schedules with variable interval 15-sec in both components, and variable interval 15-sec in one component and extinction in the other. The other two groups had identical procedures except that food was presented on a response-independent variable-time schedule. Variable-interval birds with localized stimuli showed marked behavioral contrast; variable-interval birds with non-localized stimuli showed no behavioral contrast. Variable-time birds with key-light stimuli acquired high rates of autopecking, which changed as treatment changed in a manner that paralleled rate changes, resulting in behavioral contrast for variable-interval birds. Variable-time birds with non-localized stimuli key pecked only at a low rate. The findings indicate that behavioral contrast in pigeons may result from the autopecking that is obtained with stimulus-contingent food presentation.     

A comparison of pecking generated by serial, delay, and trace autoshaping procedures

Pigeons were exposed to serial, delay, and trace autoshaping procedures. In Experiment I, all conditioned stimuli (CSs) were changes in illumination of the response key. The number of trials to acquisition of the keypeck increased from serial, to 4-sec delay, 8-sec delay, and 8-sec trace procedures, in that order. In Experiment II, which used a longer intertrial interval, trials to criterion increased from 8-sec delay, to 28-sec delay, 8-sec trace, and 28-sec trace procedures, in that order. In Experiment III, two groups received serial procedures in which the first CS was either a tone or a houselight, and the second was a keylight. The tone group acquired the key peck more rapidly than the houselight group. Early in conditioning in these experiments, and when the conditioned stimulus was a change in the keylight, there was a short latency to the onset of pecking and pecking was directed at the CS. After extensive conditioning, or when the CS was relatively diffuse, pecking still occurred, but had a longer latency and was not reliably directed toward the conditioned stimulus.     

Different gripping intervals in reproducibility of force-decreasing curve and muscle oxygenation kinetics during sustained maximal gripping

The purpose was to examine the properties and reproducibility of the force-decreasing curve and muscle-oxygenation kinetics measured by near infrared spectroscopy in sustained isometric grip and rhythmic repeated grip measurements using various contraction intervals (2 to 5 sec.). 10 healthy young adults performed both grip tests for 6 min., during which muscle-oxygenation kinetics were measured. The intraclass correlation coefficients of the time to reach the minimum value for oxygenated hemoglobin and myoglobin tended to become lower with longer relaxation time, especially over a 3-sec. interval. Although blood-flow obstruction closely influences the initial decreasing grip force during both grip tests with a 2-sec. interval, the decreasing grip force during rhythmic repeated gripping with over a 3-sec. interval is low. Hence, the physiological mechanism related to rhythmic repeated grip with over a 3-sec. interval may differ from that related to sustained isometric grip and rhythmic repeated grip with a 2-sec. interval.     

Preference and resistance to change in concurrent variable-interval schedules

Pigeons were trained on a multiple schedule in which separate concurrent schedules were presented in the two components of the schedule. During one component, concurrent variable-interval 40-sec variable-interval 80-sec schedules operated. In the second component, concurrent variable-interval 40-sec variable-interval 20-sec schedules operated. After stable baseline performance was obtained in both components, extinction probe choice tests were presented to assess preference between the variable-interval 40-sec schedules from the two components. The variable-interval 40-sec schedule paired with the variable-interval 80-sec schedule was preferred over the variable-interval 40-sec schedule paired with the variable-interval 20-sec schedule. The subjects were also exposed to several resistance-to-change manipulations: (1) prefeeding prior to the experimental session, (2) a free-food schedule added to timeout periods separating components, and (3) extinction. The results indicated that preference and resistance to change do not necessarily covary.     

The effects of number of responses on the postreinforcement pause in fixed-interval schedules

The present study manipulated the number of responses in a modified fixed-interval schedule by imposing a blackout after each unreinforced response during the interval. The blackout duration was varied, and the duration of the fixed interval was held constant. The subjects were initially exposed to a fixed-interval 300-sec schedule. Blackout durations of 0, 10, and 50 sec were used. Following this, a fixed-interval 30-sec schedule was used with blackout durations of 0, 1, and 5 sec. Under the fixed-interval 300-sec schedule, the number of interreinforcement responses varied over a wider range than occurred under the fixed-interval 30-sec schedule. The duration of the postreinforcement pause decreased as blackout durations were increased and number of responses decreased on the fixed-interval 300-sec schedule, but pause length did not vary with changes in blackout duration and number of responses for the fixed-interval 30-sec schedule. The differences in the effects of blackout duration and response manipulation on the two fixed-interval schedules were attributed to relatively greater changes in the number of interreinforcement responses for the fixed-interval 300-sec schedule.     

Role of nonreinforcement in the fixed-interval performance of pigeons

Fixed-interval (FI) schedules have been used extensively to study timing abilities. In FI schedules, animals typically show higher response rates immediately after nonreinforced (N) cycles rather than reinforced (R) cycles (the reinforcement-omission effect), and they exhibit the highest rate approximately at the time when the reinforcer is scheduled to occur (peak performance). The present experiments were designed to determine the extent to which factors other than timing contribute significantly to these two learning phenomena. Pigeons were trained in an FI 16-sec schedule in which half the cycles were R and half were N. When successive cycles were separated by a 2-sec interval, responding early in the FI interval was higher after an N cycle than after an R cycle. This reinforcement-omission effect was eliminated when the interval between cycles was increased to 12 sec, because of an increase in performance after R cycles. In addition, timing of the 16-sec interval was assessed by interpolating 32-sec test cycles (all N cycles) at two rates—either 1 test cycle every other session, or 25 test cycles per session. Peak performance, presumably indexing the animal’s ability to time the 16-sec interval, emerged only with 25 test cycles per day, but not with 1 test cycle every other day, despite extensive training with the target, 16-sec-long interval. These results suggest that transient demotivation and time-based discrimination contribute significantly to the reinforcement-omission effect and peak performance, respectively.     

Intertrial intervals and visual habituation in neonates

Eighteen 3-day-old human neonates were shown a 12 by 12 black-white checkerboard target for 45-sec. trials with either a 10-, 20-, or 30-sec. intertrial interval until their visual fixation time decreased to a set criterion for habituation. On subsequent recovery trials, a 2 by 2 black-white checkerboard target received significantly longer fixations from boys in the 10-sec. and girls in the 20-sec. conditions. 30-sec. intervals, however, produced little habituation and recovery. The implications of these findings are discussed.     

Effects of electric-shock delivery on schedule-induced water intake: delay of shock, shock intensity, and body-weight loss.

In each of four experiments, schedule-induced water intake in the rat was studied under fixed-time 40-sec food delivery. Experiments I and II studied the temporal relationship between response-independent electric-shock delivery and licking. Shock was delivered under a variable-time 60-sec schedule. A lick-dependent delay was imposed so that licking and shock delivery were systematically separated in time by a minimum of 1 to 15 sec. Over a wide range of shock intensities the data failed to reveal a consistent delay-of-shock effect. Similar shock intensities led to similar reduction of water intake at each delay of shock interval. Experiments III and IV studied the effects of body-weight loss on water intake during independent shock delivery. In Experiment III, shock was delivered under variable-time 60-sec with a minimum separation between shock and licking of 5 sec. In Experiment IV, shock was delivered under variable-time 180-sec. The minimum separation between shock and licking was 10 sec. In each study, the resistance of water intake to suppression by shock delivery increased as the degree of body-weight loss increased. Schedule-induced water intake was affected more by shock when the animal was maintained at 90% of free-feeding weight than at 70%.     

The Topography of Sexually Conditioned Behaviour: Effects of a Trace Interval

In a trace conditioning procedure, subjects were presented with a 30-sec conditioned stimulus (CS) followed by a 30-sec trace interval. Delayed conditioning consisted of a 60-sec CS presentation followed by an unconditioned stimulus (US). Although conditioning developed with both procedures, the topography of the conditioned response differed. Sexual conditioned approach was evident in all of the subjects during the presentation of the CS. Traceconditioned subjects moved away from the area where the CS had been presented during the trace interval but remained closer to the CS location than did an unpaired control. This reduction in the spatial specificity of the conditioned response was interpreted from a behaviour systems perspective. The trace interval presumably increased the perceived separation between the CS and the US and therefore elicited conditioned behaviour less specifically directed towards the CS.     

Rapid acquisition of discrete-trial lever-press avoidance: effects of signal-shock interval

Acquisition of discrete-trial lever-press avoidance learning was studied in three experiments. Experiment I compared a new training procedure, which produces rates of lever-press avoidance learning comparable to those obtained in shuttle boxes, with a “conventional”, less efficient training procedure. A factorial design was used to compare continuous versus intermittent shock and a long-variable versus a short-fixed signal-shock interval. Learning was best in the groups trained with the long and variable interval and poorest in those trained with the short and fixed interval. Type of shock had no effect. Experiment II separated the effects of duration from those of variability of the signal-shock interval. Fixed and variable intervals of 10 and 60 sec were tested and duration was the only significant factor. Experiment III addressed the effect of the differential opportunity to avoid provided by long signal-shock intervals by varying this interval from 10 to 60 sec in 10-sec steps. Only the 10-sec group showed slow acquisition relative to the others. Analysis of avoidance response latencies showed that the distributions for all groups were positively skewed and that skewness increased with increasing duration of the signal-shock interval. At intervals longer than 20 sec, the animals made progressively less use of their increased opportunity to respond. The data do not support the opportunity-to-respond interpretation of the effects of duration of signal-shock interval and suggest that some type of inhibitory process may block lever-press avoidance learning at intervals as short as 10 sec. The significance of these findings for species-specific defense reaction and preparedness theories was emphasized.     

Rapid acquisition of a sidman avoidance response

Rats were trained on a Sidman avoidance task with a 22-sec R-S and a 6-sec S-S interval for six daily 30-min training sessions. Disabling the response lever during and 0.5 sec after shock termination represented one factor in the 2 by 2 factorial design and the presentation of a feedback light cue accompanying an effective response was the other. Rats in the lever-disable condition with feedback light made significantly more avoidance responses than the other treatment groups. In a second experiment, daily 60-min sessions were observed. Using a lever-disable plus feedback light treatment, rats made more avoidance responses and received fewer shocks during the second 30-min as opposed to the first 30 min period.