Tropospheric sulfate distribution during SUCCESS: Contributions from jet exhaust and surface sources

The distribution of SO4= aerosol over the central US during SUCCESS indicates that surface sources of SO4= and SO2 in the western US caused SO4= enhancements up to 10 km altitude. The mean (median) SO4= mixing ratio in the mid- and upper-troposphere increased from 24 (16) pptv over the Pacific ocean to 58 (29) pptv over the central plains. Above 10 km the SO4=mixing ratio was essentially the same in both regions, and also when the geographic classifications were further partitioned into upper tropospheric and lower stratospheric categories (mean near 40 pptv). No obvious enhancements of SO4= could be detected in jet exhaust plumes, but this may reflect the difficulty of keeping a large airborne sampling platform within a turbulent wake for time periods longer than a few seconds. Expected SO4=enhancements (based on observed CO2 enhancements and emission factors for these two species) were generally much smaller than the variability of ambient SO4= mixing ratios, so our null result does not mean that aircraft do not emit H2SO4

Influence of vertical transport on free tropospheric aerosols over the central USA in springtime

Measurements of the atmospheric aerosol chemical composition during the Subsonic Aircraft: Contrail and Cloud Effects Special Study (SUCCESS) indicate substantial vertical transport of boundary layer aerosol to the free troposphere over the south-central United States during springtime. Mixing ratios of water-soluble aerosol Ca 2+ at 6 - 12 km altitude exhibited a median mixing ratio of 20 pptv, with 15% of the measurements \u3e 100 pptv and a maximum of ! 235 pptv. In air parcels with enhanced Ca 2+, the ratios K+/Ca 2+, Mg2+/Ca 2+, and Na+/Ca 2+ in the bulk aerosol were distinctly characteristic of those in limestone and/or cement. Significantly enhanced mixing ratios of aerosol SO42-, NO3-, and NH4 + were also concomitant with the elevated Ca 2+, suggesting transport of both crustal and anthropogenic aerosols to the upper troposphere. The mass concentration of water-soluble aerosol material was in the range 0.1 - 6 pg m -3 STP, and estimated crustal dust levels were 7 - 160 pg m \u273 ST

Reply to Proffitt, Stefanucci, Banton, and Epstein

In this reply, we acknowledge that methodological differences between the experiment of Proffitt et al. (2003) and ours might explain our failure to replicate their finding. However, we maintain that our results obtained with three different response measures point to a lack of robustness. In this reply, we acknowledge that methodological differences between the experiment of Proffitt et al. (2003) and ours might explain our failure to replicate their finding. However, we maintain that our results obtained with three different response measures point to a lack of robustness of their finding. In response to their criticism of using blind walking to measure perceived distance, we argue on theoretical grounds that blind walking, while involving post-perceptual processes, can nevertheless provide a measure of perceived distance, and then cite some of the evidence indicating that it does indeed provide such a measure.En esta réplica, los autores reconocen que las diferencias metodológicas respecto al experimento de Proffit et al. (2003) podrían explicar el fallo en la replicación. Sin embargo, se indica que la obtención de resultados negativos en tres medidas diferentes parece implicar una escasa fortaleza en el efecto. Por otra parte, y en respuesta a las críticas sobre el uso de caminar a ciegas para medir la distancia percibida, se argumenta teóricamente que esta conducta puede proporcionar una medida adecuada de la distancia percibida, aunque implique procesos posteriores a la percepción. También se cita alguna evidencia en apoyo de esta conclusión

Does Energy Expenditure Affect the Perception of Egocentric Distance? A Failure to Replicate Experiment 1 of Proffitt, Stefanucci, Banton, and Epstein (2003)

In a series of recent studies, Proffitt and his colleagues have reported that the perceived distance to a target is influenced by the energy expenditure associated with any action, such as walking or throwing, for spanning the distance to the target. In particular, Proffitt, Stefanucci, Banton, and Epstein (2003) reported that wearing a heavy backpack caused verbal reports of distance to increase. We conducted a study to determine whether three responses dependent on perceived distance (verbal report of distance, blind walking, and estimates of object size) are influenced by the backpack manipulation. In two experiments, one involving a between-participants design and the other involving a within participants design, we found that none of the three responses were influenced by the wearing of a heavy backpack.En una serie reciente de trabajos, Proffitt y sus colegas informaron de que la distancia a la que se percibe una estimulación diana se ve afectada por el gasto de energía asociado a la realización de cualquier acción, como andar o lanzar un objeto, que pueda realizarse para cubrir la distancia hasta la estimulación diana. Concretamente, Proffitt, Stefanucci, Banton y Epstein (2003) afirmaron que llevar una mochila pesada hizo que se incrementasen los informes verbales sobre la distancia. Realizamos un estudio para verificar si tres respuestas que dependen de la distancia percibida (informe verbal de distancia, andar a ciegas y estimaciones del tamaño de un objeto) son afectadas por el uso de la mochila. En dos experimentos, uno con un diseño inter-participantes y el otro con un diseño intra-participantes, encontramos que ninguna de las tres respuestas era afectada por llevar una mochila pesada

Basic and applied research relating to auditory displays for visually impaired people

Proceedings of the 9th International Conference on Auditory Display (ICAD), Boston, MA, July 7-9, 2003.This paper describes basic and applied research, conducted mostly by Roberta Klatzky, Reginald Golledge, and the author, in connection with development of a navigation system for visually impaired people. The paper begins with a treatment of the issues involved in achieving effective sensory substitution. It then discusses the importance of distance perception in spatial hearing, compares spatial language and real sound in their effectiveness in creating stable mental representations of environmental locations, and ends with a review of research on the display component of the navigation system user interface

Active localization of virtual sounds

We describe a virtual sound display built around a 12 MHz 80286 microcomputer and special purpose analog hardware. The display implements most of the primary cues for sound localization in the ear-level plane. Static information about direction is conveyed by interaural time differences and, for frequencies above 1800 Hz, by head sound shadow (interaural intensity differences) and pinna sound shadow. Static information about distance is conveyed by variation in sound pressure (first power law) for all frequencies, by additional attenuation in the higher frequencies (simulating atmospheric absorption), and by the proportion of direct to reverberant sound. When the user actively locomotes, the changing angular position of the source occasioned by head rotations provides further information about direction and the changing angular velocity produced by head translations (motion parallax) provides further information about distance. Judging both from informal observations by users and from objective data obtained in an experiment on homing to virtual and real sounds, we conclude that simple displays such as this are effective in creating the perception of external sounds to which subjects can home with accuracy and ease

Combining Locations from Working Memory and Long-Term Memory into a Common Spatial Image

This research uses a novel integration paradigm to investigate whether target locations read in from long-term memory (LTM) differ from perceptually encoded inputs in spatial working-memory (SWM) with respect to systematic spatial error and/or noise, and whether SWM can simultaneously encompass both of these sources. Our results provide evidence for a composite representation of space in SWM derived from both perception and LTM, albeit with a loss in spatial precision of locations retrieved from LTM. More generally, the data support the concept of a spatial image in working memory and extend its potential sources to representations retrieved from LTM

Spatial working memory for locations specified by vision and audition: Testing the amodality hypothesis

Spatial working memory can maintain representations from vision, hearing, and touch, representations referred to here as spatial images. The present experiment addressed whether spatial images from vision and hearing that are simultaneously present within working memory retain modality-specific tags or are amodal. Observers were presented with short sequences of targets varying in angular direction, with the targets in a given sequence being all auditory, all visual, or a sequential mixture of the two. On two thirds of the trials, one of the locations was repeated, and observers had to respond as quickly as possible when detecting this repetition. Ancillary detection and localization tasks confirmed that the visual and auditory targets were perceptually comparable. Response latencies in the working memory task showed small but reliable costs in performance on trials involving a sequential mixture of auditory and visual targets, as compared with trials of pure vision or pure audition. These deficits were statistically reliable only for trials on which the modalities of the matching location switched from the penultimate to the final target in the sequence, indicating a switching cost. The switching cost for the pair in immediate succession means that the spatial images representing the target locations retain features of the visual or auditory representations from which they were derived. However, there was no reliable evidence of a performance cost for mixed modalities in the matching pair when the second of the two did not immediately follow the first, suggesting that more enduring spatial images in working memory may be amodal