Eric R. Jensen's research while affiliated with University of California, Berkeley and other places

Natural killer (NK) cells attack many tumour cell lines, and are thought to have a critical role in anti-tumour immunity; however, the interaction between NK cells and tumour targets is poorly understood. The stimulatory lectin-like NKG2D receptor is expressed by NK cells, activated CD8+ T cells and by activated macrophages in mice. Several distinct cell-surface ligands that are related to class I major histocompatibility complex molecules have been identified, some of which are expressed at high levels by tumour cells but not by normal cells in adults. However, no direct evidence links the expression of these 'induced self' ligands with tumour cell rejection. Here we demonstrate that ectopic expression of the murine NKG2D ligands Rae1beta or H60 in several tumour cell lines results in potent rejection of the tumour cells by syngeneic mice. Rejection is mediated by NK cells and/or CD8+ T cells. The ligand-expressing tumour cells induce potent priming of cytotoxic T cells and sensitization of NK cells in vivo. Mice that are exposed to live or irradiated tumour cells expressing Rae1 or H60 are specifically immune to subsequent challenge with tumour cells that lack NKG2D ligands, suggesting application of the ligands in the design of tumour vaccines.

With headphones, the perceived lateral position of one frequency band (the target) can be affected by the presence of a second band with different interaural parameters (the interferer). This binaural interference persists despite a stimulus onset asynchrony (SOA) from interferer to target of up to 320 ms [L. R. Bernstein and C. Trahiotis, J. Acoust. Soc. Am. 94, 735?742 (1993)]. The current study presented targets and interferers in anechoic space from pairs of speakers chosen from an array of 12. A visual pointer was used to indicate the perceived location of the target. Localization of a sinusoidally amplitude?modulated (SAM) target (carrier = 500 Hz, modulator = 250 Hz) was unaffected by the presence of an SAM interferer (carrier = 4000 Hz). When the target was the higher frequency, however, there were large individual differences, with some listeners showing interference while others did not. Unlike the studies with headphones, when interference was seen a distractor to target SOA of only 40 ms was sufficient to eliminate the interference. [Work supported by a grant from the NIH, NIDCD 00087.]

Increasing the distance to an acoustic source produces: (a) low‐pass filtering of the spectrum through absorption by the medium, (b) reduction in the overall sound‐pressure level of the stimulus, and (c) changes in the temporal and directional relations between sounds along the primary acoustic pathway and those on secondary pathways (echoes). A simulated open‐field environment [Hafter et al., J. Acoust. Soc. Am. 92, 2334 (1992)] consisting of an anechoic chamber and multiple computer‐controlled speakers was used to study the discriminability of changes in distance. Simulated acoustic reflections were from a single, fully reflective wall. Assuming spectral cues would be ineffective with small changes of distance, the primary concern was with the roles of level and echoes. Other considerations included the changing temporal overlap of primary and secondary stimuli for lengthening trains of wideband, midfrequency (4‐kHz center) impulses, and distance perception for single words and short phrases. Subjects reported that with echoes they always heard a change in distance, but without echoes, they heard either a change in distance orloudness. Thresholds were smallest when the changes were interpreted as distance, thus performance was generally better with echoes.

The effects of echoes on azimuthal discrimination and localization in the lateral plane were studied using single wide band clicks. Over much of the frontal quadrant, echoes decreased discrimination by no more than a factor of 2, though effects were greater near the aural axis. In general, localizations were of perceptually fused images closer to the source than the echo, but for large echo delays, the image sometimes broke into parts.

Virtual auditory environments are generally created by filtering stimuli through head‐related transfer functions that mimic reflections and resonances of the shoulders, head, and external ears, and then presenting the sounds through earphones. Here, a different approach has been adopted in which multiple loudspeakers are used in an anechoic chamber to create virtual sources and echoes in space. Individual digital filters are used to equalize the loudspeakers and the computer/interface system allows for creation of multiple virtual sources and echoic surfaces. The locations of sources and echoic surfaces can be roved from trial to trial over a wide range of distances and over the eight separate azimuths allowed by the apparatus. Spatial discrimination is measured with two‐alternative forced choice psychophysics while, for localization, subjects use a laser pointer to indicate the directions of apparent sources. For wideband clicks (cf=4 kHz), these results show that the presence of single echoes increases spatial thresholds by a factor of about 2 across the range of source azimuths from 0° to 90°. The pointing data show that apparent locations of the sources are moved toward those of the echoes by about 4° to 5°, a result that is unaffected by the magnitudes of the source–echo separation in either azimuth (8° to 40°) or delay (1 to 30 ms). At longer delays, subjects sometimes report double images, one near the direction of the source and the other near that of the echo.