The dimensional nature of same-different discrimination behavior in pigeons

We studied the dimensional nature of same-different discrimination behavior in pigeons. Birds first learned to discriminate between simultaneously presented displays of 16 identical items (Same arrays) and 16 nonidentical items (Different arrays), conditional on the color of the background. After discrimination mastery, we tested the birds with Mixture arrays comprising both identical and nonidentical items. Accuracy increased and reaction time decreased as the disparity in entropy (a measure of variability) between the arrays increased. As well, within each entropy disparity level, lower entropy values were more discriminable than higher entropy values. These results accord with a logarithmic relation between entropy and discriminative behavior and, thus, with the idea that the discrimination of Same from Different arrays follows Weber's Law.     

The Role of Death Qualification in Venirepersons' Attitudes Toward the Insanity Defense1

Three hundred venirepersons from the 12^th Judicial Circuit in Florida completed a booklet of stimulus materials that contained the following: one question that specified participants' level of support for the death penalty; one Witt death‐qualification question; a case scenario that included a summary of the guilt and penalty phases of a capital case; verdict and sentencing preferences; a 16‐item measure that required participants to rate their receptiveness to the insanity defense on a 6‐point Likert scale; and standard demographic questions. Results indicated that death‐qualified venirepersons, when compared to excludables, were more likely to endorse certain insanity myths, find the defendant guilty, and sentence the defendant to death. Legal implications are discussed.     

The Standard Objection to the Standard Account

Philosophical Studies - What is the relation between a clay statue andthe lump of clay from which it is made? According to the defender of the standardaccount, the statue and the lump are...     

Limited attention and cue order consistency affect predictive learning: a test of similarity measures

The authors empirically tested the similarity metrics underlying 2 predictive-learning theories: J. K. Kruschke's (1992) attention learning covering map and J. M. Pearce's (1987, 1994) configural models. In Experiment 1, participants concurrently learned 3 types of discriminations: simple (A- vs. B+), common cue (XC- vs. XD+), and compound (YE- vs. ZF+). Accuracy was ordered: simple > compound > common cue. Neither model anticipated this ordering. In Experiment 2, cue order in 2-element configurations was either inconsistent (e.g., YE and EY) as in Experiment 1 or consistent (e.g., EY throughout). Although accuracy differences were smaller under consistent ordering, the relative difficulty of the tasks was the same as in Experiment 1. In Experiment 3, common cue and compound discriminations were tested in different participants to determine whether the ordering of difficulty in Experiments 1 and 2 was caused by differential generalization mediated by the number of elements; the ordering was the same as in Experiments 1 and 2. These results suggest the need for differential attention to event presence and absence and to mechanisms that incorporate limited attentional capacity.     

Recent advances in operant conditioning technology: A versatile and affordable computerized touchscreen system

We report the construction of a new operant chamber that incorporates modern computer, touchscreen, and display technologies. An LCD display was housed in the front wall of a lightweight Plexiglas chamber. An Apple eMac computer was used to present visual stimuli on the monitor and to control other chamber events. Responses to the stimuli were recorded using a transparent resistive-type touchscreen that overlaid the monitor. The resulting system is simple and inexpensive to construct but powerful and flexible enough to explore a broad range of issues in animal learning and behavior.     

Effects of occlusion on pigeons' visual object recognition

Casual observation suggests that pigeons and other animals can recognize occluded objects; yet laboratory research has thus far failed to show that pigeons can do so. In a series of experiments, we investigated pigeons' ability to 'name' shaded, textured stimuli by associating each with a different response. After first learning to recognize four unoccluded objects, pigeons had to recognize the objects when they were partially occluded by another surface or when they were placed on top of another surface; in each case, recognition was weak. Following training with the unoccluded stimuli and with the stimuli placed on top of the occluder, pigeons' recognition of occluded objects dramatically improved. Pigeons' improved recognition of occluded objects was not limited to the trained objects but transferred to novel objects as well. Evidently, the recognition of occluded objects requires pigeons to learn to discriminate the object from the occluder; once this discrimination is mastered, occluded objects can be better recognized.     

Display variability and spatial organization as contributors to the pigeon's discrimination of complex visual stimuli

Three experiments assessed the contributions of display variability and spatial organization to the pigeon's discrimination of 16-icon visual displays. After training to discriminate 4 x 4 arrays of same and different computer icons, 4 pigeons were shown testing displays that systematically manipulated the variability of the depicted icons and their spatial organization on the display screen. Display variability and spatial organization each reliably controlled the pigeon's behavior. These seemingly separate effects could be collectively explained by the pigeon's discriminating the amount of variability or entropy in localized regions of the display.     

Effects of number of items on the baboon's discrimination of same from different visual displays

Three experiments explored the baboon's discrimination of visual displays that comprised 2 to 24 black-and-white computer icons; the displayed icons were either the same as (same) or different from one another (different). The baboons' discrimination of same from different displays was a positive function of the number of icons. When the number of icons was decreased to 2 or 4, the baboons responded indiscriminately to the same and different displays, exhibiting strong position preferences. These results are both similar to and different from those of pigeons that were trained and tested under comparable conditions. Accepted after revision: 23 May 2001 Electronic Publication     

Pigeons' recognition of partially occluded objects depends on specific training experience

DiPietro et al (2002 Perception 31 1299-1312) reported a dramatic improvement in pigeons' recognition of partially occluded objects after the birds had been trained to recognize objects that were placed on top of another surface. Here, we investigated whether training with partially erased stimuli or with notched stimuli that had a thin gap between the object and another surface would similarly enhance pigeons' recognition of partially occluded objects. We found that erased training had no effect on the birds' recognition of partially occluded objects. Training pigeons to recognize notched objects improved their performance with the same objects when they were partially occluded; but this improvement did not transfer to novel objects, a result that DiPietro et al reported after on-top training. Together, the present results and those of DiPietro et al implicate prior experience as a key factor in pigeons' recognition of partially occluded objects. Training experiences which improve recognition of partially occluded objects may do so because they improve decomposition of complex two-dimensional scenes by pigeons into separate entities.