Backward blocking: the role of within-compound associations and interference between cues trained apart

Most theoretical accounts of backward blocking place heavy stress on the necessity of the target cue having been trained in compound with the competing cue to produce a decrement in responding. Yet, other evidence suggests that a similar reduction in responding to the target cue can be observed when the outcome is later paired with a novel cue never trained in compound with the target cue (interference between cues trained apart). The present experiment shows that pairing another nonassociated cue with the same outcome may be sufficient to produce a decremental effect on the target cue, but the presence of a within-compound association between the target and the competing cue adds to this effect. Thus, both interference between cues trained apart and within-compound associations independently contribute to backward blocking.     

The Future Similarity Objection Revisited

David Lewis has long defended an analysis of counterfactuals in terms of comparative similarity of possible worlds. The purpose of this paper is to reevaluate Lewis’s response to one of the oldest and most familiar objections to this proposal, the future similarity objection.     

Prior experience affects amodal completion in pigeons

In a three-alternative forced-choice task, 4 pigeons were trained to discriminate a target stimulus consisting of two colored shapes, one of which partially occluded the other, from two foil stimuli that portrayed either a complete or an incomplete version of the occluded shape. The dependent measure was the percentage of total errors that the birds committed to the complete foil. At the outset of training, the pigeons committed approximately 50% of total errors to the complete foil, but as training progressed, the percentage of errors to the complete foil rose. When the pigeons were given a second exposure to the initial set of stimuli, they committed 70% of total errors to the complete foil, suggesting that they now saw the complete foil as more similar to the occluded target than the incomplete foil. These results suggest that experience with 2-D images may facilitate amodal completion in pigeons, perhaps via perceptual learning.     

Pigeons and people select efficient routes when solving a one-way "traveling salesperson" task

The authors presented people (Experiment 1) and pigeons (Experiments 2 and 3) with a large number of 1-way traveling salesperson problems that consisted of 3, 4, and 5 identical stimuli (nodes) on a computer monitor. The sequence of nodes that each traveler selected was recorded, and the distance of the route was subsequently determined. The routes the pigeons and people selected were reliably more efficient than those used by a Monte Carlo model given the same problems. The pigeons' routes were significantly less efficient than a nearest neighbor model of performance, however. In Experiment 3, pigeons were required to select a route that was within the top 33% of all possible solutions for a given problem. The pigeons' solutions were significantly more efficient than those observed in Experiment 2, in which the behavioral criterion was not imposed. The mechanisms that pigeons and people may have been using to solve the traveling salesperson problems are discussed.     

Limulus psychophysics: dark adaptation in the ventral eye.

Sudden illumination applied to Limulus produces an unconditioned downward tail movement which is under stimulus control and can be used to measure psychophysical thresholds. The method of constant stimuli was used to measure the behavioral dark-adaptation function mediated by the ventral eye of Limulus. The resulting function has two phases, each of which is rectified when log threshold is made a function of long time in the dark. Under the conditions of the present experiment, the transition between the two phases occurred at 6 min. This psychophysical dark-adaptation function has the same form as an electrophysiologic dark-adaptation function obtained by Fein and DeVoe (using the ventral eye receptor potential as the response). In more complex visual systems such two-phase, dark-adaptation functions would usually be interpreted in terms of screening pigment movements or changes in the neural contributions of different receptor classes, but neither interpretation is appropriate for the ventral eye of Limulus.     

The disruption of autoshaped key pecking in the pigeon by food-tray illumination

Two experiments investigated the effect of food-tray illumination on pecking a lighted key that signalled food presentation. Pigeons key pecked less when both feeder and key stimuli preceded grain delivery than when the keylight alone signalled food. This detractive influence of grain-tray illumination did not result after prior pairings of the keylight with food. The involvement of associative and physical variables in autoshaping the pigeon's key peck is considered in light of these findings.     

Perceived duration,visual persistence,and neural integration

Varying stimulus intensity while measuring the perceived duration/visual persistence of brief light flashes has yielded disparate results. Some studies have found a direct relationship between the two variables; others have found an inverse relationship. Several models have been suggested to unify this behavioral literature. They invoke the absolute intensity and the nature of the judgment as explanatory variables. We now present physiological data whose analysis was motivated by these models. We measured the duration of photoreceptor potentials as a function of light intensity and response measure. One response measure was. the length of time required for the response to decline from the peak by a criterion amount. The other response measure was the length of time a response stayed above a criterion level. These data suggest that each behaviorally based model captured a different aspect of a single underlying mechanism and that a melding of the two critical concepts would harmonize all of the results: In this melding, the sensory signals that mediate visual perception would have the type of complex intensity- and time-dependent properties found in real neural responses.     

Intensity dependence of perceived duration: data, theories, and neural integration

Evaluates 2 theoretical models suggested to explain studies of the effect of stimulus intensity on the perceived duration of brief light flashes. Some studies found a direct relationship between the 2 variables; others found an indirect relationship. Each model suggests that an additional variable interacts with stimulus intensity. Proposed variables have included the nature of the judgment and the absolute intensity. The present evaluation indicates that both of the proposed variables play a role and that a melding of the models could best account for this phenomenon. The melding incorporates known time- and intensity-dependent characteristics of neural integration into the behavioral performance. The evaluation also indicates that future experiments on this problem will be most informative if they (a) give particular attention to the role of instructions, (b) explore an adequate range of intensities, and (c) strictly control adaptive state.     

Further remarks on the role of cognition in the comparative analysis of behavior

Recent interest in comparative psychology has stimulated much research and debate concerning cognitive processes in animal behavior. The present paper relates to this general area by treating particular issues in the analysis of comparative cognition: specifically, how cognition is inferred from animal behavior; whether the postulation of intervening cognitive processes furthers our understanding of behavior; and how rival approaches help advance the science of behavior.