An eyewitness paradox

Two methods of analysing data from an identification parade give rise to seemingly contradictory outcomes, both of which reach statistical significance. The traditional method is based on the first choices of eyewitnesses, whereas the paired-comparison method takes account of each eyewitness's full rank ordering of the lineup participants. The person that most eyewitnesses pick out as the perpetrator of an offence (according to the first-choice method) may in fact be the person that those same eyewitnesses as a group regard as least likely to have committed the act (according to the paired-comparison method). Implications of the paradox for the analysis of lineup data are considered.     

Molecular maximizing characterizes choice on Vaughan's (1981) procedure

Pigeons keypecked on a two-key procedure in which their choice ratios during one time period determined the reinforcement rates assigned to each key during the next period (Vaughan, 1981). During each of four phases, which differed in the reinforcement rates they provided for different choice ratios, the duration of these periods was four minutes, duplicating one condition from Vaughan's study. During the other four phases, these periods lasted six seconds. When these periods were long, the results were similar to Vaughan's and appeared compatible with melioration theory. But when these periods were short, the data were consistent with molecular maximizing (see Silberberg & Ziriax, 1982) and were incompatible with melioration, molar maximizing, and matching. In a simulation, stat birds following a molecular-maximizing algorithm responded on the short- and long-period conditions of this experiment. When the time periods lasted four minutes, the results were similar to Vaughan's and to the results of the four-minute conditions of this study; when the time periods lasted six seconds, the choice data were similar to the data from real subjects for the six-second conditions. Thus, a molecular-maximizing response rule generated choice data comparable to those from the short- and long-period conditions of this experiment. These data show that, among extant accounts, choice on the Vaughan procedure is most compatible with molecular maximizing.     

CORRESPONDENCE TRAINING: AN EXAMPLE OF RULE-GOVERNED BEHAVIOR?

Two groups of six mentally retarded adults were exposed to either a “say/do” correspondence training program or a “do only” reinforcement procedure to evaluate the suggestion of Rogers-Warren and Baer (1976) that reinforcement of the nonverbal target behavior in the absence of the relevant verbal behavior may account for the behavior changes seen in correspondence training. The participants worked in an experimental setting on a variety of manipulatory responses leading to various auditory and visual consequences. Analysis of individual patterns of responding indicated no apparent differences between the groups during training; four individuals in each group appeared to develop generalized correspondence skills. We conclude that the outcome of correspondence training may not necessarily be verbal regulation of behavior as is assumed. Rather, we suggest that the notion of rule-governed behavior can best account for the type of behavior changes seen in correspondence studies.     

Choice between reliable and unreliable outcomes: mixed percentage-reinforcement in concurrent chains.

Pigeons' choices between alternatives that provided different percentages of reinforcement in mixed schedules were studied using the concurrent-chains procedure. In Experiment 1, the alternatives were terminal-link schedules that were equal in delay and magnitude of reinforcement, but that provided different percentages of reinforcement, with one schedule providing, reinforcement twice as reliably as the other. All pigeons preferred the more reliable schedule, and their level of preference was not systematically affected by variation in the absolute percentage values, or in the magnitude of reinforcement. In Experiment 2, preference for a schedule providing 100% reinforcement over one providing 33% reinforcement increased systematically with increases in the duration of the terminal links. In contrast, preference decreased systematically with increases in the duration of the initial links. Experiment 3 examined choice with equal percentages of reinforcement but unequal delays to reinforcement. Preference for the shorter delay to reinforcement was not systematically affected by variation in the absolute percentage of reinforcement. The overall pattern of results supported predictions based on an extension of the delay-reduction hypothesis to choice procedures involving mixed schedules of percentage reinforcement.     

Reply to silberberg and ziriax

Silberberg and Ziriax (1985) report that a modification of Vaughan's (1981) procedure produces results inconsistent with melioration (the position advocated by Vaughan) but consistent with a process they term molecular maximizing. Here it is argued that the theory of molecular maximization is not sufficiently unambiguous that researchers other than the developers can test its predictions, and that in any case none of the data presented by Silberberg and Ziriax are both clearly consistent with molecular maximization and inconsistent with melioration.     

More on concurrent interval-ratio schedules: a replication and review.

It has been suggested that the failure to maximize reinforcement on concurrent variable-interval, variable-ratio schedules may be misleading. Inasmuch as response costs are not directly measured, it is possible that subjects are optimally balancing the benefits of reinforcement against the costs of responding. To evaluate this hypothesis, pigeons were tested in a procedure in which interval and ratio schedules had equal response costs. On a concurrent variable time (VT), variable ratio-time (VRT) schedule, the VT schedule runs throughout the session and the VRT schedule is controlled by responses to a changeover key that switches from one schedule to the other. Reinforcement is presented independent of response. This schedule retains the essential features of concurrent VI VR, but eliminates differential response costs for the two alternatives. It therefore also eliminates at least one significant ambiguity about the reinforcement maximizing performance. Pigeons did not maximize rate of reinforcement on this procedure. Instead, their times spent on the alternative schedules matched the relative rates of reinforcement, even when schedule parameters were such that matching earned the lowest possible overall rate of reinforcement. It was further shown that the observed matching was not a procedural artifact arising from the constraints built into the schedule.     

A temporal limit on the effect of future food on current performance in an analogue of foraging and welfare

Rats obtained access to food twice each 24-hour period. The first session was a work session in which food was available on a progressive-ratio schedule. During the second session, which occurred between 1 and 23 hours after the work session, food was freely available up to a fixed total intake each 24 hours. The situation resembled elements of several real world circumstances, including the choice between continuing to forage in a rapidly depleting patch and waiting for a better patch, and between working now and receiving a guaranteed income later. The purpose of the experiment was to explore the time period over which future access to reward could affect current responding. Contrary to what might be expected from recent theorizing, anticipation of future food delayed by an hour or more after the start of the work session had no effect on current performance. Food intake was high and constant during work sessions except for a prefeeding effect that occurred when the free session closely preceded the next day's work session. Also, an increase in the difficulty of the work schedule increased the amount of work and the maximum price paid for food as if the work session were the only time food was available. The results indicate the importance of considering temporal limits in theories that require animals to integrate input over time to determine the allocation of resources among alternatives.     

Behavior regulation and learned performance: Some misapprehensions and disagreements

The behavior-regulation approach to learned performance has been the subject of misapprehension and disagreement concerning: (1) the nature and importance of behavior regulation, (2) the definition and role of behavioral set-points, (3) the relation of optimal schedule performance to behavioral set-points, and (4) the question of whether deviations from total responding or from response patterns are the primary determinant of molar responding under schedule constraint. After clarifying the nature and role of behavior regulation and set-points, this paper shows that the data used to question optimal schedule performance (Allison, 1981a) actually strongly support the general behavior-regulation approach. These data also indicate a role for response-pattern set-points in determining schedule behavior, but contradict the hypothesis that deviations from response-pattern characteristics are the primary determinant of molar schedule effects.