Spatial delayed matching-to-sample performance by rats: Learning, memory, and proactive interference.

Nine Sprague-Dawley rats were trained in a 3-alternative delayed matching-to-sample task in which the samples were rewarded forced choices of 1 arm of a 3-arm starburst maze, and retention was indicated by returning to that arm following a delay or retention interval. If the S made an error on its 1st free choice of a trial, the chosen arm was blocked off, and the S was allowed a 2nd choice between the remaining 2 arms. Ss quickly acquired this task. Exp II showed that choice accuracy was lower with 1-min retention intervals than with immediate tests. In Exp III, there was evidence for 2 separable proactive interference effects. The degree to which prior events influenced responding decreased as the intertrial interval increased. Choice accuracy improved with increasing intertrial interval and declined with increasing retention interval durations. Additionally, choice accuracy was higher when the sample from the previous trial matched the sample from the current trial and lower when they did not match. These results suggest that encoding information about visited spatial locations is a gradual process rather than an all-or-none process in rats. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Human listeners provide insights into echo features used by dolphins (Tursiops truncatus) to discriminate among objects.

Echolocating bottlenose dolphins (Tursiops truncatus) discriminate between objects on the basis of the echoes reflected by the objects. However, it is not clear which echo features are important for object discrimination. To gain insight into the salient features, the authors had a dolphin perform a match-to-sample task and then presented human listeners with echoes from the same objects used in the dolphin's task. In 2 experiments, human listeners performed as well or better than the dolphin at discriminating objects, and they reported the salient acoustic cues. The error patterns of the humans and the dolphin were compared to determine which acoustic features were likely to have been used by the dolphin. The results indicate that the dolphin did not appear to use overall echo amplitude, but that it attended to the pattern of changes in the echoes across different object orientations. Human listeners can quickly identify salient combinations of echo features that permit object discrimination, which can be used to generate hypotheses that can be tested using dolphins as subjects. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Atlantic bottlenose dolphin (Tursiops truncatus) hearing threshold for brief broadband signals.

The hearing sensitivity of an Atlantic bottlenose dolphin (Tursiops truncatus) to both pure tones and broadband signals simulating echoes from a 7.62-cm water-filled sphere was measured. Pure tones with frequencies between 40 and 140 kHz in increments of 20 kHz were measured along with broadband thresholds using a stimulus with a center frequency of 97.3 kHz and 88.2 kHz. The pure-tone thresholds were compared with the broadband thresholds by converting the pure-tone threshold intensity to energy flux density. The results indicated that dolphins can detect broadband signals slightly better than a pure-tone signal. The broadband results suggest that an echolocating bottlenose dolphin should be able to detect a 7.62-cm diameter water-filled sphere out to a range of 178 m in a quiet environment. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Object representation in the bottlenose dolphin (Tursiops truncatus): integration of visual and echoic information

A dolphin performed a 3-alternative matching-to-sample task in different modality conditions (visual/echoic, both vision and echolocation: visual, vision only; echoic, echolocation only). In Experiment 1, training occurred in the dual-modality (visual/echoic) condition. Choice accuracy in tests of all conditions was above chance without further training. In Experiment 2, unfamiliar objects with complementary similarity relations in vision and echolocation were presented in single-modality conditions until accuracy was about 70%. When tested in the visual/echoic condition, accuracy immediately rose (95%), suggesting integration across modalities. In Experiment 3, conditions varied between presentation of sample and alternatives. The dolphin successfully matched familiar objects in the cross-modal conditions. These data suggest that the dolphin has an object-based representational system.     

Recognition of aspect-dependent three-dimensional objects by an echolocating Atlantic bottlenose dolphin.

We examined the ability of a bottlenose dolphin (Tursiops truncatus) to recognize aspect-dependent objects using echolocation. An aspect-dependent object such as a cube produces acoustically different echoes at different angles relative to the echolocation signal. The dolphin recognized the objects even though the objects were free to rotate and sway. A linear discriminant analysis and nearest centroid classifier could classify the objects using average amplitude, center frequency, and bandwidth of object echoes. The results show that dolphins can use varying acoustic properties to recognize constant objects and suggest that aspect-independent representations may be formed by combining information gleaned from multiple echoes. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Matching-to-sample by an echolocating dolphin (Tursiops truncatus).

An adult male dolphin was trained to perform a three-alternative delayed matching-to-sample task while wearing eyecups to occlude its vision. Sample and comparison stimuli consisted of a small and a large plastic tube, a water-filled stainless steel sphere, and a solid aluminum cone. Stimuli were presented under water and the dolphin was allowed to identify the stimuli through echolocation. The echolocation clicks emitted by the dolphin to each sample and each comparison stimulus were recorded and analyzed. Over 48 sessions of testing, choice accuracy averaged 94.5% correct. This high level of accuracy was apparently achieved by varying the number of echolocation clicks emitted to various stimuli. Performance appeared to reflect a pre-experimental stereotyped search pattern that dictated the order in which comparison items were examined and a complex sequential-sampling decision process. A model for the dolphin's decision-making processes is described. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Anger, impulsivity, and anger control in combat-related posttraumatic stress disorder.

Examined the association of combat-related posttraumatic stress disorder (PTSD) with anger. 24 veterans of the Vietnam War with PTSD scored significantly higher on an Anger factor comprising multiple measures of anger than did comparison groups of 23 well-adjusted Vietnam combat veterans and 12 noncombat Vietnam-era veterans with psychiatric diagnoses. In contrast, the 3 groups did not differ significantly on orthogonal factors, one of which comprised cognitive impulsivity measures and the other of which reflected motor impulsivity. Changes in heart rate in response to provocation loaded positively on the Anger factor and negatively on the 2 Impulsivity factors. Concurrent depression and trait anxiety did not have an effect on level of anger in individuals with PTSD. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Sequential effects in pigeon delayed matching-to-sample performance.

Five pigeons were tested in a 3-alternative delayed matching-to-sample task in which 2nd choices were permitted following 1st-choice errors. Sequences of responses both within and between trials were examined in 3 experiments. In Exp I, the sample information contained in 1st-choice errors was not sufficient to account for the observed pattern of 2nd choices. This implies that 2nd choices following 1st-choice errors are based on a 2nd examination of the contents of working memory. Proactive interference was found in Exp II in the form of a dependency, beyond that expected on the basis of trial-independent response bias, of 1st-choices from 1 trial on the 1st-choice emitted on the previous trial. Samples from the previous trial did not exert a significant influence on later trials. The magnitude of the intertrial association (Exp III) did not depend on the duration of the intertrial interval. In contrast, longer intertrial intervals and longer sample durations facilitated choice accuracy by strengthening the association between current samples and choices. Results are incompatible with a trace-decay and completion model; they suggest that multiple influences act simultaneously and independently to control delayed matching-to-sample responding. These influences include memory for the choice occurring on the previous trial, memory for the sample, and general effects of trial spacing. (32 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)