Herbert L. Roitblat

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

Empirical evidence of a relationship between combat-related PTSD and increased anger is lacking. In this study, 24 veterans of the Vietnam War with posttraumatic stress disorder (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. These empirical findings support and extend the clinical evidence regarding PTSD and anger.

OBJECT RECOGNITION THROUGH EAVESDROPPING : PASSIVE ECHOLOCATION IN BOTTLENOSE DOLPHINS

A bottlenose dolphin (Tursiops truncatus) demonstrated the ability to select the matching object in a matching-to-sample task after listening to another dolphin inspect the sample object via echolocation. The listener was prevented from inspecting the sample himself. In Experiment 1, with objects familiar to both dolphins, the listener’s performance was significantly better than chance. In Experiment 2, objects familiar to only one of the dolphins were used. On these trials, the listener’s performance was significantly better than chance only when the inspecting dolphin made a correct choice. Analysis of the listener’s responses when the inspector made an error demonstrated that this contingency was not due to the listener’s matching the inspector’s response, but was apparently due instead to inadequate information in the echo. The results suggest that the listener was able to “eavesdrop” on echoes produced by the inspector’s clicks and derive characteristics of the sample object.

Sonar recognition of targets embedded in sediment

Abstract Dolphins have biological sonar abilities that exceed those of any man-made system in an aquatic environment. One problem of particular importance, and for which only limited capabilities exist, is the detection and recognition of targets buried under sediment. This paper reviews dolphin echolocation capabilities and describes a system that uses a dolphin-like signal and biomimetic signal processing mechanisms to emulate the performance of the dolpin on such targets. The system employed a digitized dolphin click with a center frequency of 120 kHz and a 3dB bandwidth of 39 kHz, 50 μs duration. This signal was transmitted through seawater into mud and the echoes reflected from the objects were recorded and digitized. Two spectral estimators were used to extract a time-frequency representation of the echo. One was based on short-time fast Fourier transforms, and the other was based on an autoregressive estimator. The time-frequency representation was then processed by a separate backpropagation neural network for each estimator, designed to derive independent identifications of the targets. These identifications were then combined in a modified probabilistic neural network that used a linear transfer function rather than a binary function for its output. Finally the output of the probabilistic network was processed symbolically by a simple expert system. Three experiments are described in which the system was used to discriminate a small stainless-steel cylinder from cyliners of the same size made of hollow aluminium, foam-filled aluminium, or coral rock embedded in resin. Each of the targets was presented buried in mud at a depth of several centimeters. The system proved highly effectively at recognizing these buried targets.

Recognizing successive dolphin echoes with an integrator gateway network

Abstract An novel network architecture, the integrator gateway network, was developed to classify multiple successive echoes from targets ensonified by a dolphins natural echolocation signal in a naturalistic environment. The inputs to the network were spectral vectors of the returning echo plus one unit representing the start of each scan. This network combined information from successive echoes returning from the same target and reset between scans of different targets. The network was trained on a small subset (4%) of the total set of available echoes (1,335). Depending on the measure used to assess it, the network correctly classified between 90–93% of all echo trains. In contrast, a standard back propagation network with the same number of units and variable connections as in the integrator gateway network performed with only about 63% accuracy in classifying echo trains. The integration model seems to provide a better account of the dolphins performance than a decision model that does not combine information from multiple echoes. Although it does not prove that dolphins similarly combine information from multiple echoes, in the absence of relevant neurophysiological evidence, it provides support for such a hypothesis. It also suggests the potential beneifts to be derived for pattern recognition from combining multiple samples from the same target.

Generalization of visual matching and delayed matching by a California sea lion (Zalophus californianus)

Only a limited number of species have been found capable of generalized matching-to-sample (MTS) after exposure to relatively few training exemplars. We trained a juvenile, experimentally naive California sea lion (Zalophus californianus) in MTS, using a pair of three-dimensional objects as samples. Successful matching to a criterion of 90% correct or better over 2 successive sessions was attained in 12 sessions (269 trials and 70 errors). Two subsequent “partial” transfer tests, in which each of the two training objects was paired with a novel test object, and four additional transfer tests, all with novel objects, were presented following training. An 80% performance criterion over 2 successive sessions was reached, or closely approximated, in from 2 to 4 transfer sessions for all transfer tests; errors to criterion tended to be reduced across the successive novel transfer tests and were as few as five during the final two tests; and performance on the first 48 trials of the last two novel transfers was not significantly different from a near-ceiling level baseline performance measure. Neophobic responses of the sea lion to new objects precluded an unbiased evaluation of immediate (Trial 1) transfer. The sea lion’s short-term memory for sample objects was also measured. Matching performance was maintained at a level of 78% correct responses or better for delays through to 45 sec after removal of the sample object. At a 58-sec delay, the longest tested, performance declined to 69% correct responses. These retention levels are only somewhat below levels reported for dolphins and nonhuman primates tested on visual delayed MTS, but they are above levels typically reported for pigeon subjects.

Compelled attention: the effects of viewing trauma-related stimuli on concurrent task performance in posttraumatic stress disorder.

We examined the ability of Vietnam veterans with PTSD to focus attention on a primary digit detection task while concurrently viewing neutral or Vietnam-related picture and word distractors. Controlling for combat exposure, military service, and psychopathology, veterans with PTSD took longer to detect the target when Vietnam-related pictures were distractors. There were no reaction time differences when word stimuli were distractors. The latency effect was specific to trials with trauma-related pictures and did not spread to neutral trials interleaved within a mixed block of trauma and neutral pictures. Individuals with PTSD recalled proportionally more Vietnam-related words than other groups, implying differential attention to Vietnam-related words. Attending to trauma-related pictures interferes with performance of a concurrent task by individuals with PTSD.

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.

The Structure of Events

Until recently the paradigm representation for animals was a reflex and a copy. A simple stimulus is detected and a simple response results. Learning, it would follow, would correspond to the formation of connections between these stimuli and responses. Internal changes resulting from experience were thought to mirror the corresponding physical events about which the animal was learning (Bolles, 1975). In such a paradigm it is difficult to conceive of how an animal would represent a complex or structured event. Considerable research effort was dedicated to discovering the simple stimulus properties that mediated performances that otherwise appeared to involve complex events (see Roitblat, 1987, for a review). The goal was to explain these apparently complex events by discovering the simple properties to which the animal was actually responding. The investigator could thereby reduce the apparently complex event to a simple one.

The Honolulu posttraumatic stress disorder stimulus set

We present word and picture stimuli constituting a validated stimulus set appropriate for cognitive investigations of posttraumatic stress disorder (PTSD). Combat related and neutral words and pictures were rated by Vietnam veterans with PTSD and by three comparison groups along four dimensions: unpleasantness, Vietnam relevance, stressfulness, and memorability. There were distinctive patterns of responses by the PTSD group which efficiently discriminated the individuals in this group from those in the control groups. These stimuli have the potential to be developed as a diagnostic instrument.

Animal echolocation and signal processing

The echolocation capabilities of dolphins and small whales exceed those of current man-made sonars. Dolphins, beluga whales and false killer whales can perceive small targets presented over 110 m away, can classify target shapes independent of internal target reverberation, can discriminate wall thickness differences in targets of less than .2 mm, and can operate in high noise environments. Recent natural observations indicate that several species may also detect and choose targets buried in sediment. These tasks are accomplished through the use of range-gated clicks that tend to be broad band with peak frequencies exceeding 100 kHz. The short (50 microsec) pulses can have amplitudes exceeding 220 db and bandwidths exceeding 60 kHz. This paper provides a short review of animal echolocation capabilities, methodologies used to examine them, and potential uses of neural networks and other signal processing techniques to understand and perhaps duplicate those animal capabilities.<<ETX>>