Biomedical subjects

William A Roberts

Publications and source records attributed to William A Roberts.

14 recordsLinked to original sources

PubMed2006

Testing for episodic-like memory in rats in the absence of time of day cues: replication of Babb and Crystal.

Two experiments were performed to look for evidence of episodic-like memory in rats. On each of a series of trials on an eight-arm radial maze, rats in two groups entered four open arms in Phase 1, with reward pellets on three arms and a favored reward (chocolate in Experiment 1 and cheese in Experiment 2) on the remaining arm. Phase 2 retention tests were given 30 min or 4 h after Phase 1, with all eight arms open. The four arms not entered in Phase 1 all contained reward pellets, and the three arms that contained pellets in Phase 1 were empty. In the replenish short group, the favored reward was replenished at the same location where it was found in Phase 1 at the 30 min retention interval but was absent (Experiment 1) or degraded (Experiment 2) at the 4 h retention interval. In the replenish long group, the favored reward was replenished at the 4 h retention interval but not at the 30 min retention interval. Over a number of daily trials that randomly mixed short and long delays, rats in both experiments learned to return earlier to the arm containing the favored reward at the retention interval when it was replenished than at the retention interval when it was absent or degraded. These results replicate earlier findings [Babb, S.J., Crystal, J.D., 2005, Discrimination of what, when, and where: implications for episodic-like memory in rats. Learn. Mot., 36, 177-189] and provide evidence of episodic-like memory in rats.

Analysis of Variance↗

PubMed2006

Animal memory: episodic-like memory in rats.

Recent experiments with rats on a radial maze indicate that they can remember what foods they encountered, and when and where they encountered them. These findings, and others with food-storing birds, challenge the idea that only humans have episodic memory.

Animals↗

PubMed2006

Evidence that pigeons represent both time and number on a logarithmic scale.

Pigeons were presented with trials that always began with presentation of a houselight that lasted for 1-16s. Red and green side keys were presented immediately after the houselight went off. A peck on the red key was reinforced if the houselight duration was 8s or shorter, and a peck on the green key was reinforced if the houselight duration was 9s or longer. Plots of asymptotic performance as a function of houselight duration showed bow-shaped curves with higher accuracy at the ends of the scale than in the middle. Training to bisect a scale containing houselight durations of 2-32s yielded a performance curve that superimposed on the 1-16s curve. Both curves showed two important asymmetries around the midpoint: pigeons were more accurate at 9 and 10s than at 7 and 8s but were more accurate at 1-4s than at 13-16s. These findings closely resembled those found in a similar study of number scale bisection [Roberts, W.A., 2005. How do pigeons represent numbers? Studies of number scale bisection. Behav. Process. 69, 33-43]. Theoretical predictions from associative and confusion models showed a good match to the obtained data if it was assumed that time and number scales were logarithmic and that generalization or confusion curves were constant but not if it was assumed that scales were linear and that generalization or confusion curves were scalar.

Animals↗

PubMed2006

Do dogs (Canis familiaris) seek help in an emergency?

The question of whether dogs recognize an emergency and understand the need to seek help from a bystander was tested in two experiments. In the first experiment, dogs' owners feigned a heart attack in an open field, and in the second experiment, dogs' owners experienced an accident in which a bookcase fell on them and pinned them to the floor. In these experiments, one or two bystanders were available to which dogs could go for help. The dogs' behavior was taped for 6 min after the owner had fallen and was later scored for the frequency and time the dogs spent performing different behaviors. In no case did a dog solicit help from a bystander. It is concluded that dogs did not understand the nature of the emergency or the need to obtain help.

Animals↗

PubMed2006

Anticipation of future events in squirrel monkeys (Saimiri sciureus) and rats (Rattus norvegicus): tests of the Bischof-Kohler hypothesis.

The Bischof-Kohler hypothesis holds that nonhuman animals cannot anticipate a future event and take appropriate action when that event involves satisfaction of a need not currently experienced. Tests of the Bischof-Kohler hypothesis were performed with squirrel monkeys (Saimiri sciureus) and rats (Rattus norvegicus). In experimental trials with both species, a nonthirsty animal had its water bottle removed and then chose between a smaller and larger quantity of food. Consumption of the food induced thirst. Choice of the smaller quantity led to the return of the water bottle sooner than choice of the larger quantity. Monkeys reversed their baseline preference for the larger quantity of food when the experimental contingencies were introduced, but rats continued to prefer the larger amount. Although the rat findings support the Bischof-Kohler hypothesis, the monkey findings challenge it.

Animals↗

PubMed2005

How do pigeons represent numbers? Studies of number scale bisection.

Pigeons' bisection of two number scales, 1-16 and 2-32, was examined in two experiments. In Experiment 1, pigeons learned to choose different comparison keys following 1 or 16 key pecks and 2 or 32 key pecks and then were tested with intermediate numbers of key pecks on nonreinforced probe trials. Psychophysical curves that plotted choice of the large number key against number of pecks showed superposition of the two number scales and indifference between the two keys at the geometric means of each scale. The same procedures were used in Experiment 2, but pigeons were trained to bisect each scale at its arithmetic mean. Two asymmetries appeared in curves that plotted discrimination performance against number: near the midpoints of the scales, accuracy was higher for high numbers than for low numbers, but this relationship reversed at the ends of the scales, with low numbers discriminated more accurately than high numbers. An associative model that assumed stimulus generalization between numbers was used to predict the findings of these two experiments. The model showed a good qualitative fit to the obtained data when it was assumed that number was represented on a log scale and generalization was constant at all numbers but not when it was assumed that number was represented on a linear scale and generalization was scalar.

Animals↗

PubMed2004

Can squirrel monkeys (Saimiri sciureus) plan for the future? Studies of temporal myopia in food choice.

In seven experiments, 2 squirrel monkeys were given choices between arrays of food that varied in the quantity offered. In Experiments 1-5, the monkeys were offered choices between quantities of the same food that varied in a 2:1 ratio. The squirrel monkeys failed to show the temporal myopia effect or a decrease in preference for the larger quantity as the absolute number of food items offered increased. Even when given choices of 8 versus 16 peanuts and 10 versus 20 peanuts, both monkeys significantly preferred the larger quantity. An examination of the monkeys' rates of consumption indicated that 20 peanuts were consumed over a 1- to 2-h period, with eating bouts separated by periods of nonconsumption. In Experiments 6A, 6B, and 7, food was either pilfered or replenished 15 min after an initial choice, so that choice of the smaller quantity led to more total food in the long run. These manipulations caused both monkeys to reduce choice of the larger quantity, relative to baseline choice. The results suggest that squirrel monkeys anticipated the future consequences of their choices.

Animals↗

PubMed2003

Spatial memory for food hidden by rats (Rattus norvegicus) on the radial maze: studies of memory for where, what, and when.

Rats (Rattus norvegicus) were allowed to hide food items on an 8-arm radial maze by carrying the items from the center to boxes at the end of each arm. Retrieval tests given after rats had hidden 4 items showed that they selectively returned to the maze arms where food had been hidden (Experiments 1 and 2). When rats were allowed to hide pieces of cheese (refed food) and pretzels (less preferred food) on different arms, they both hid and retrieved cheese before pretzels (Experiments 2-5). In Experiment 6, rats chose between arms where cheese and pretzels were hidden,with cheese degraded at one delay interval but not the other. Together, these experiments indicate memory for what and where but not when.

Animals↗

PubMed2003

Human nonverbal counting estimated by response production and verbal report.

In three experiments, people were shown sequential displays and were prevented from verbal counting by being required to perform other cognitive tasks. In Experiment 1, the subjects were shown three target (target = 8, 16, or 32) sequences of colored geometric shapes. On occasional question trials, the subjects were asked to estimate the target number after the final item in the sequence. On other test trials, items continued to appear beyond the target, and the subjects estimated the target manually by tapping a space bar. In Experiments 2 and 3, a matching-to-sample procedure required the subjects to estimate the same sequence of items (target = 8, 11, 14, 17, or 20) both verbally and manually. The results indicated that (1) manual and verbal estimates closely approximated target size in Experiments 1 and 2, (2) coefficients of variation were constant across target size, and (3) correlations between manual and verbal estimates were positive in Experiments 2 and 3. Requiring the subjects to perform a counting task during presentation of items led to underestimation of number in Experiment 3.

Adult↗

PubMed2002

Are animals stuck in time?

People can time travel cognitively because they can remember events having occurred at particular times in the past (episodic memory) and because they can anticipate new events occurring at particular times in the future. The ability to assign points in time to events arises from human development of a sense of time and its accompanying time-keeping technology. The hypothesis is advanced that animals are cognitively stuck in time: that is, they have no sense of time and thus have no episodic memory or ability to anticipate long-range future events. Research on animals' abilities to detect time of day, track short time intervals, remember the order of a sequence of events, and anticipate future events are considered, and it is concluded that the stuck-in-time hypothesis is largely supported by the current evidence.

Animals↗

PubMed2002

Two tests of the stuck-in-time hypothesis.

The authors report 2 experiments that test the stuck-in-time hypothesis, which argues that animals cannot time-date events and thus do not remember when events occurred and do not anticipate future events. In Experiment 1, rats in the experimental condition could earn a large reward by reentering the 1st arm that they visited on a radial maze. They did not learn to reenter this arm early and did no better than did a control group that was not given a large reward for reentering the first arm. In Experiment 2, rats in the experimental group could earn a large reward by delaying entry into a distinctive arm. These rats did not learn to delay entry into the distinctive arm, and they performed no better than did the control-group rats, which did not receive a large reward for delayed entry. These experiments provide further evidence in support of the stuck-in-time hypothesis.

Animals↗

PubMed2002

Failure to find evidence of stimulus generalization within pictorial categories in pigeons.

Pigeons' key pecks were reinforced in the presence of pictures from one of two categories, cats or cars. A single picture associated with reinforcement was used in Experiment 1, and 20 pictures from the same category were associated with reinforcement in Experiment 2. Pigeons then were presented with novel test pictures from the training category and from the other, previously unseen, category. During Session 1 of testing, pigeons pecked no more often at pictures from the reinforced category than at pictures from the previously unseen category. When pigeons were trained with pictures associated with reinforcement or its absence from different categories in Experiment 3, differential responding to novel pictures from different categories appeared during Session 1. These findings argue against a process of automatic stimulus generalization within natural categories and in favor of the position that category distinctions are not made until members of at least two categories are compared with one another.

Animals↗

PubMed2002

On the determinants of induction in responding for sucrose when food pellet reinforcement is upcoming.

Rats' rates of leverpressing for low-concentration liquid-sucrose reinforcers in the first half of an experimental session increase when food pellet, rather than sucrose, reinforcers will be available in the second half. Experiment 1 determined that this induction effect was the outcome of food pellet reinforcement's increasing response rates, not of continued sucrose reinforcement's decreasing them. Experiments 2 and 3 showed that induction was primarily controlled by the conditions of reinforcement in the current session, not by those in the previous one. Experiment 4 showed little evidence that the induction was the outcome of Pavlovian processes. These results suggest that induction may occur because of processes operating at the level of the entire session. They also provide a link to a seemingly related area of study: contrast effects. Some of the results are consistent with what is known about contrast effects, but there are also several, yet unexplained differences.

Animals↗

PubMed2002

Pigeons presented with sequences of light flashes use behavior to count but not to time.

On randomly ordered trials, pigeons were presented with either a blue or a white key that flashed red for 200 ms at a fast (2 flashes/s), medium (1 flash/s), or slow (0.5 flashes/s) rate. The blue key signaled a fixed-interval (FI) schedule in which the first response after 20 s was reinforced, and the white key signaled a fixed-number (FN) schedule in which the first response after 20 flashes was reinforced. In Experiments 1 and 2, pigeons showed depressed responding to the flash on FI-cued trials and accelerated responding to the flash on FN-cued trials. When the response key was periodically blacked out in Experiments 3 and 4, counting but not timing was eliminated.

Animals↗