The sound localization ability of human observers has been frequently examined in quiet environments, but there have been relatively few studies that have considered the effect of noise on sound localization. In this study, three subjects judged the perceived direction of broadband click-train signal in the quiet and in the presence of a broadband noise at nine signal-to-noise ratios, which varied over a 23 dB range. The signal could originate from any of 239 spatial locations that completely surrounded the subjects in azimuth 360 degrees) and ranged from -45 degrees to (+)90 degrees in elevation; the masker (when present) was always located directly in front of the subjects at 0 degrees azimuth and 0 degree elevation. The subjects indicated the perceived direction of the signal by pointing at a 20-cm-diam spherical model of auditory space. As the signal-to-noise ratio was lowered, the accuracy of localization judgments decreased nearly monotonically. However, the accuracy of judgments relative to the median plane (i.e., the left/right dimension) was less strongly influenced by the presence of noise than was the accuracy of judgments relative to the horizontal plane (i.e., the up/down dimension). The accuracy of judgments relative to the frontal plane (i.e., the front/back dimension) was most strongly influenced by noise.

Many human-computer interfaces are designed with the assumption that the user must adapt to the system, that users must be trained and their behavior altered to fit a given interface. The research presented here proceeds from the alternative assumption: Novice behavior is inherently sensible, and the computer system can be made to adapt to it. Specifically, a measurably easy-to-use interface was built to accommodate the actual behavior of novice users. Novices attempted an electronic mail task using a command-line interface containing no help, no menus, no documentation, and no instruction. A hidden operator intercepted commands when necessary, creating the illusion of an interactive session. The software was repeatedly revised to recognize users' new commands; in essence, the interface was derived from user behavior. This procedure was used on 67 subjects. The first version of the software could recognize only 7 percent of all the subjects' spontaneously generated commands; the final version could recognize 76 percent of these commands. This experience contradicts the idea that user input is irrelevant to the design of command languages. Through careful observation and analysis of user behavior, a mail interface unusable by novices evolved into one that let novices do useful work within minutes.

Atechnique is described for rapidly collecting responses in auditory-localization experiments. Subjects indicate the perceived direction of the sound by pointing at a 20-cm-diam spherical model. In Experiment 1, the subjects judged the direction of a broadband signal, which could originate from any of 239 directions ranging through 360 0 of azimuth and between -45 0 and +90 0 of elevation, Using this technique, the subjects responded 2-8 times more rapidly than previous subjects who used either a verbal-reporting technique or a head-pointing technique. Localization judgments were as accurate as they had been with verbal reports, but were not as accurate as judgments collected using the head-pointing technique. In Experiment 2, the signal was turned off and the experimenter read the spherical coordinates of the signal location to the subjects, The subjects pointed to these coordinates more accurately than they had judged the direction of the sounds in Experiment 1, suggesting that the response technique had not been the limiting factor in that experiment. Circumstances relevant to the choice of response techniques for auditory-localization experiments are discussed, There has been a recent resurgence of interest in the phenomena of human sound localization (

Do immigrant outflows lead to native inflows? An empirical analysis of the migratory responses to US state immigration legislation * Michael Good † I estimate the impact on population and employment for 52 different demographic groups of the recent influx of state omnibus immigration laws targeting undocumented immigrants in the United States. I find evidence that while the demographic groups pinpointed as having higher percentages of undocumented individuals certainly experience population and employment 'outflows' from states implementing these immigration laws, there is a lack of associated 'inflows' for those demographic groups identified by economic theory as being probable substitutes for undocumented immigrants. Several segments designated as probable substitutes actually experience an adverse effect on population and employment. This finding provides rigorous empirical backing to existing anecdotal evidence of the same migratory phenomenon, resulting in clear policy implications in relation to the ongoing debate over immigration. * I acknowledge support provided by the Horowitz Foundation for Social Policy and Florida International University's Presidential Fellowship. I thank Cem Karayalcin for useful discussion.

As three-dimensional auditory displays become more prevalent, there will be an increasing need to understand the interactions that can be expected among spatially separated sounds. A two-alternative, forced-choice, adaptive staircase procedure was used to measure the detectability of a 165-ms click-train signal masked by a continuous Gaussian noise, as a function of the spatial separation between the signal and the masker in the free field. Horizontal separations within the horizontal plane and vertical separations within the median plane were examined for low-, mid-, and high-frequency stimuli. Masking was reduced by as much as 18 dB when the signal and masker were separated horizontally. Sizable reductions in masking (6-9 dB) were also observed for vertical separations. The largest reductions in masking were observed for the high-frequency stimuli. The data are compared with the results of headphone-based studies of binaural masking. Implications for the design of auditory displays are considered.