Asymmetric performance in the cocktail party effect: implications for the design of spatial audio displays.

An experiment was conducted to determine the extent to which hemispheric specialization is manifested in the performance of tasks in which listeners are required to attend to one of several simultaneously spoken speech communications. Speech intelligibility and response time were measured under factorial combinations of the number of simultaneous talkers, the target talker hemifield, and the spatial arrangement of talkers. Intelligibility was found to be mediated by all of the independent variables. Results are discussed in terms of the design of adaptive spatial audio interfaces for speech communications. Actual or potential applications of this research include the design of adaptive spatial audio interfaces for speech communications.

Auditory localization under sustained +Gz acceleration.

The ability to localize a virtual sound source in the horizontal plane was evaluated under varying levels of sustained (+Gz) acceleration. Participants were required to judge the locations of spatialized noise bursts in the horizontal plane (elevation 0 degrees) during exposure to 1.0, 1.5, 2.5, 4.0, 5.5, and 7.0 +Gz. The experiment was conducted at the U.S. Air Force Research Laboratory's Dynamic Environment Simulator, a three-axis centrifuge. No significant increases in localization error were found between 1.0 and 5.5 +Gz; however, a significant increase did occur at the 7.0 +Gz level. In addition, the percentage of front/back confusions did not vary as a function of +Gz level. Collectively, these results indicate that the ability to localize virtual sound sources is well maintained at various levels of sustained acceleration. Actual or potential applications include the incorporation of spatial audio displays into the human-computer interface for vehicles that are operated in acceleration environments.

Ipsilateral loudness adaptation over multiple intensity levels.

Could monaural loudness adaptation be a simple artifact of psychophysical contrast? From adaptation data based on the Ipsilateral Comparison Paradigm (ICP), A. J. Dange, J. S. Warm, E. M. Weiler, and W. N. Dember (1993) concluded that loudness adaptation was not an artifact of psychophysical contrast, but their conclusion was dependent on results from one intensity. This study, involving multiple intensities, re-examined the issue of contrast versus adaptation and generally supported the conclusions of Dange et al. The results also showed an unexpected asymmetry of adaptation based on the direction of the referent modulation used with the ICP technique. Some implications are discussed.

Effects of localized auditory information on visual target detection performance using a helmet-mounted display.

An experiment was conducted to evaluate the effects of localized auditory information on visual target detection performance. Visual targets were presented on either a wide field-of-view dome display or a helmet-mounted display and were accompanied by either localized, nonlocalized, or no auditory information. The addition of localized auditory information resulted in significant increases in target detection performance and significant reductions in workload ratings as compared with conditions in which auditory information was either nonlocalized or absent. Qualitative and quantitative analyses of participants' head motions revealed that the addition of localized auditory information resulted in extremely efficient and consistent search strategies. Implications for the development and design of multisensory virtual environments are discussed. Actual or potential applications of this research include the use of spatial auditory displays to augment visual information presented in helmet-mounted displays, thereby leading to increases in performance efficiency, reductions in physical and mental workload, and enhanced spatial awareness of objects in the environment.

Target detection performance in helmet-mounted and conventional dome displays.

An experiment was conducted to assess visual target detection performance using a helmet-mounted display (HMD) and a conventional flight simulation dome display. Measures of workload and mood were also obtained. Participants in both viewing conditions scanned an area 120 degrees vertical by 240 degrees horizontal while attempting to locate targets that appeared to be approaching them from one of a possible 18 locations. Results indicated significantly superior performance in the conventional dome display. Workload and mood measures also showed a significant advantage for the dome display. Results are discussed in terms of their implications for the design and use of HMD systems as components of airborne virtual environment interfaces.

Nicotine self-administration in rats.

Female Wistar rats were allowed to self-administer nicotine solutions through indwelling jugular vein cannulae for 23 h per day for periods from three to five weeks. Two response levers were available to the rats; responding on one lever, designated the active lever, produced an immediate infusion of nicotine solution or saline. A second lever for which responding had no programmed consequences was introduced as a control for the locomotor stimulant action of low doses of nicotine. Baseline lever response rates were determined over a period of one week, in which active lever responding produced an infusion of saline. Rats were then allowed access to varying doses of nicotine or saline for a further two or three weeks. Response rates on the active lever increased significantly in rats with access to nicotine at a dose of 30 micrograms kg-1 per response. However, control lever response rates were also significantly elevated. The role of nicotine-induced locomotor stimulation in the self-administration behaviour was further evaluated in a dose-reduction experiment, in which the dose of nicotine available to rats responding for 30 micrograms kg-1 per response was reduced to 3 micrograms kg-1 per response. This resulted in a significant differential increase in active lever responding relative to control lever responding. The results suggest that nicotine is positively reinforcing in rats which had not previously been deprived of food or water or received prior drug treatment, but also indicate that nicotine induced locomotor stimulation may contribute to the observed increases in lever response rates when rats self-administer nicotine.

Brain site variations in effects of morphine on electrical self-stimulation.

Pairs of bipolar electrodes were stereotaxically aimed at two of three sites: the locus coeruleus (LC), the substantia nigra, pars compacta (SNC), and the median forebrain bundle (MFB). Rats were shaped to bar-press for trains of intracranial electrical stimulation presented as pairs of monophasic pulses. The first pulse of a pair (the C, conditioning pulse) was followed by a second pulse (the T, test pulse) after a parametrically varied interval. The effects of chronic morphine administration were tested in a paradigm of 7 days saline, 7 days morphine, 1 day morphine+naloxone, and 6 days post-drug saline. High doses of morphine (5 mg/kg) depressed response rates for intracranial self-stimulation (ICSS). LC placements and those just lateral or ventral to the LC showed large increases in ICSS rates under morphine (2.5 mg/kg). This area was delimited on either side by tips that showed response rate depressions under morphine. MFB placements yielded response rate facilitations under morphine. Sites medial to the MFB and ventral within the MFB showed rate depressions under morphine. Dorsal substantia nigra placements showed facilitated rates, whereas placements ventral within the SNC and substantia nigra, pars reticulata (SNR) produced more variable results, with rates tending to be depressed by morphine. The ICSS procedure may be a useful animal model for detecting the abuse potential of drugs.

Morphine and intracranial self-stimulation in the hypothalamus and dorsal brainstem: differential effects of dose, time and site.

The purpose of this study was to examine if morphine, a drug of abuse, exerts site-specific effects on intracranial self-stimulation (ICSS). Rats, implanted with dorsal brainstem (DB) and hypothalamic (HYP) electrodes, bar-pressed for ICSS at two current intensities eight hours a day during six days each of predrug saline, morphine (2.5, 5.0, 7.5 or 10.0 mg/kg) and postdrug saline conditions. There were three patterns of drug effects: "pure" depressions, "pure" facilitations and a biphasic pattern (depressions followed by facilitations). Repeated morphine administration modified the temporal patterning of these effects: shortened duration of depressions and produced earlier onsets of facilitations. Within an animal, DB electrodes displayed more depressions than the HYP electrodes. Tolerance to the depressant effects, observed frequently, occurred occasionally to the facilitative effects of morphine. The drug effects on ICSS were dissociated from those observed on other behavioral measures, and thus are not artifacts of concomitant changes in activity levels.

Intracranial self-stimulation site specificity: the myth of current spread.

Locus-specificity of intracranial self-stimulation (ICSS) was determined for 78 electrode placements using monophasic stimulation. ICSS rate comparisons between each pole of a bipolar electrode when each served as cathode were made when the anodal source was either the other pole of the bipolar electrode or a skull screw. In hypothalamic areas, medial forebrain bundle electrode tips elicited significantly higher rates than electrode tips of the same bipolar electrodes located in perifornical or far-lateral diencephalic placements. In turn, perifornical electrode tips elicited higher rates than more dorsally or medially placed tips. In dorsal pontine areas, locus coeruleus electrode tips elicited significantly higher rates than more medially or laterally placed tips. In periaqueductal midbrain and substantia nigra placements, tips located along the midline or in the substantia nigra elicited significantly higher rates than tips located lateral to or ventral to those respective structures. Anodal locus did not change these results. These results suggest that ICSS behavior is delimited by and corresponds to neuroanatomically discrete entities and that cathodal, rather than anodal factors seem to most crucially determine ICSS integrity.