Cues to food location that domestic dogs (Canis familiaris) of different ages do and do not use

The results of three experiments are reported. In the main study, a human experimenter presented domestic dogs (Canis familiaris) with a variety of social cues intended to indicate the location of hidden food. The novel findings of this study were: (1) dogs were able to use successfully several totally novel cues in which they watched a human place a marker in front of the target location; (2) dogs were unable to use the marker by itself with no behavioral cues (suggesting that some form of human behavior directed to the target location was a necessary part of the cue); and (3) there were no significant developments in dogs’ skills in these tasks across the age range 4 months to 4 years (arguing against the necessity of extensive learning experiences with humans). In a follow-up study, dogs did not follow human gaze into “empty space” outside of the simulated foraging context. Finally, in a small pilot study, two arctic wolves (Canis lupus) were unable to use human cues to locate hidden food. These results suggest the possibility that domestic dogs have evolved an adaptive specialization for using human-produced directional cues in a goal-directed (especially foraging) context. Exactly how they understand these cues is still an open question. Received: 28 April 2000 / Accepted after revision: 2 September 2000     

Effects of instructional constraints on human fixed-interval performance

Several groups of human subjects were exposed to a variety of experimental conditions involving a fixed-interval 27-second schedule of reinforcement in compound with instructions to constrain in the number of responses within the interreinforcement interval and/or the duration of the experimental session. One group was further exposed to a contingency involving the placement of responses within the IRI. A diversity of patterns of performance was observed, including those typically associated with animal subjects exposed to FI schedules. Generally, the imposition of instructions to minimize session duration reduced post-reinforcement pausing and increased overall reinforcement density from those levels obtained with only instructions to expend a given number of responses per reinforcer. The results are seen to underscore the sensitivity of human fixed-interval performance and the contribution of extra-experimental contingencies.     

Prepositional phrases spoken and heard

The relation between verbal and nonverbal behavior with common syntactic properties was investigated, using retarded and nonretarded children. Reinforcement was contingent on either verbal or nonverbal responses whereas responses of the other repertoire had no experimental consequences. Changes sometimes occurred in the unreinforced (collateral) repertoire, but they were always changes in the stimulus control of pre-existing topographies. A contingency involving responses of one repertoire never instated new topographies in the collateral repertoire. This suggested that the problem of “cross-modality generalization” should be reformulated to distinguish explicitly between instating new topographies and changing the stimulus control of pre-existing topographies. The result confirmed Skinner's hypothesis about “the same response spoken and heard” and clarified some anomalies in previous studies.     

THE MODIFICATION OF LEISURE BEHAVIOR IN A HALF-WAY HOUSE FOR RETARDED WOMEN1

A multi-element baseline design combined with a multiple-baseline design, was used to investigate the effect of availability of materials, prizes for participation, and instruction on the leisure behavior of 14 mentally retarded women in a half-way house. A leisure program was conducted on weekday evenings, during which residents could choose to participate in any of six activities offered: puzzles, card games, clay, painting, weaving, and rug making. It was found that instruction in weaving and rug making significantly increased the percentage of residents participating in these activities, and that following instruction, prizes were not necessary to maintain high levels of participation. In contrast, prizes were more effective than mere availability of materials in maintaining participation in the other activities.     

Effects of social context, reinforcer probability, and reinforcer magnitude on humans' choices to compete or not to compete.

In the first two experiments, subjects' choices to earn points (exchangeable for money) either by competing with a fictitious opponent or by not competing were studied. Buskist, Barry, Morgan, and Rossi's (1984) competitive fixed-interval schedule was modified to include a second response option, a noncompetitive fixed-interval schedule. After choosing to enter either option, the opportunity for reinforcers became available after the fixed-interval's duration had elapsed. Under the no-competition condition, points were always available after the interval had elapsed. Under the competition condition, points were available based on a predetermined probability of delivery. Experiments 1 and 2 examined how reinforcer probabilities and reinforcer magnitudes affected subjects' choices to compete. Several general conclusions can be made about the results: (a) Strong preferences to compete were observed at high and moderate reinforcer probabilities; (b) competing was observed even at very low reinforcer probabilities; (c) response rates were always higher in the competition component than in the no-competition component; and (d) response rates and choices to compete were insensitive to reinforcer-magnitude manipulations. In Experiment 3, the social context of this choice schedule was removed to determine whether the high levels of competing observed in the first two experiments were due to a response preference engendered by the social context provided by the experimenters through instructions. In contrast to the first two experiments, these subjects preferred the 60-s fixed-interval schedule (formerly the no-competition option), indicating that the instructions themselves were responsible for the preference to compete. This choice paradigm may be useful to future researchers interested in the effects of other independent variables (e.g., drugs, social context, instructions) on competitive behavior.     

Instructed versus shaped human verbal behavior: Interactions with nonverbal responding

Undergraduate students' presses on left and right buttons occasionally made available points exchangeable for money. Blue lights over the buttons were correlated with multiple random-ratio random-interval components; usually, the random-ratio schedule was assigned to the left button and the random-interval to the right. During interruptions on the multiple schedule, students filled out sentence-completion guess sheets (e.g., The way to earn points with the left button is to...). For different groups, guesses were shaped with differential points also worth money (e.g., successive approximations to “press fast” for the left button), or were instructed (e.g., Write “press slowly” for the left button), or were simply collected. Control of rate of pressing by guesses was examined in individual cases by reversing shaped or instructed guesses, by instructing pressing rates, and/or by reversing multiple-schedule contingencies. Shaped guesses produced guess-consistent pressing even when guessed rates opposed those characteristic of the contingencies (e.g., slow random-ratio and fast random-interval rates), whereas guesses and rates of pressing rarely corresponded after unsuccessful shaping of guesses or when guessing had no differential consequences. Instructed guesses and pressing were inconsistently related. In other words, when verbal responses were shaped (contingency-governed), they controlled nonverbal responding. When they were instructed (rule-governed), their control of nonverbal responding was inconsistent: the verbal behavior sometimes controlled, sometimes was controlled by, and sometimes was independent of the nonverbal behavior.     

Shaping data collection congruent with experimental hypotheses

The influence of instructions and feedback from an experimenter on observational recordings of disruptive behavior was evaluated. Four subject-observers recorded four categories of disruptive behavior from videotapes of children in a classroom setting. Two sets of videotapes, labelled "baseline" and "treatment", were matched for rates of disruptive behavior in each category. The observers were told that two target behaviors were expected to decrease and the other two control behaviors were not expected to change during the treatment condition. During observational recording of treatment videotapes, the observers were given positive feedback when they reported decreases in the two target behaviors, and negative feedback when they reported either to change or increases in the two control behaviors. The target behaviors were recorded less frequently by observers, while recordings of control behaviors were unaffected during the treatment phase. These results suggest that contingent feedback to observers should be avoided as a possible source of bias in behavioral recordings.     

Chimpanzees’ (Pan troglodytes) use of gaze cues in object-choice tasks: different methods yield different results

To assess the influence of different procedures on chimpanzees' performance in object-choice tasks, five adult chimpanzees were tested using three experimenter-given cues to food location: gazing, glancing, and pointing. These cues were delivered to the subjects in an identical fashion but were deployed within the context of two distinct meta-procedures that have been previously employed with this species with conflicting results. In one procedure, the subjects entered the test unit and approached the experimenter (who had already established the cue) on each trial. In the other procedure, the subjects stayed in the test unit throughout a session, witnessed the hiding procedure, and waited for a delay of 10 s during which the cue was provided. The subjects scored at high levels far exceeding chance in response to the gaze cue only when they approached the experimenter for each trial. They performed at chance levels when they stayed inside the test unit throughout the session. They scored at chance levels on all other cues irrespective of the procedure. These findings imply that (a) chimpanzees can immediately exploit social gaze cues, and (b) previous conflicting findings were likely due to the different meta-procedures that were used.     

‘Please sort these voice recordings into 2 identities’: Effects of task instructions on performance in voice sorting studies

We investigated the effects of two types of task instructions on performance on a voice sorting task by listeners who were either familiar or unfamiliar with the voices. Listeners were asked to sort 15 naturally varying stimuli from two voice identities into perceived identities. Half of the listeners sorted the recordings freely into as many identities as they perceived; the other half were forced to sort stimuli into two identities only. As reported in previous studies, unfamiliar listeners formed more clusters than familiar listeners. Listeners therefore perceived different naturally varying stimuli from the same identity as coming from different identities, while being highly accurate at telling apart the stimuli from different voices. We further show that a change in task instructions – forcing listeners to sort stimuli into two identities only – helped unfamiliar listeners to overcome this selective failure at ‘telling people together’. This improvement, however, came at the cost of an increase in errors in telling people apart. For familiar listeners, similar non-significant trends were apparent. Therefore, even when informed about correct number of identities, listeners may fail to accurately perceive identity further highlighting that voice identity perception in the context of natural within-person variability is a challenging task. We discuss our results in terms of similarities and differences to findings in the face perception literature and their importance in applied settings, such as forensic voice identification.