02299nas a2200121   4500008004100000245008200041210006900123520186900192100001802061700001602079700002602095856005602121       2005                        eng d00aThe start of phonotactic walking in the fly Ormia ochracea: a kinematic study0 astart of phonotactic walking in the fly Ormia ochracea a kinemat3 a<p>Ormia ochracea (Diptera, Tachinidae) are acoustic parasitoids of crickets that have one of the most directionally sensitive auditory systems known. We studied dynamic characteristics of walking phonotaxis in these flies in response to variations in sound source azimuth, and compared phonotaxis of flies in freely walking conditions to tethered flies walking on a treadmill. Motor patterns at the initiation of phonotaxis are not stereotyped even for similar stimulus conditions. Flies respond to directional sound sources by walking in a tight curve that combines rotation and forward translation until they are oriented towards the source direction, then continue on a straight path. Translational velocity accelerates throughout the duration of the stimulus then decelerates following stimulus offset. In contrast, rotational velocity accelerates and then decelerates within the duration of the stimulus such that flies have completed the rotational component of the response and reached&nbsp;their final heading before the end of the stimulus. Rotational velocity is the only response parameter that varies systematically with sound source direction (azimuth). Differences in the amplitude of rotational velocity as a function of source azimuth determine the directional orientation of phonotactic responses. The relationship between rotational velocity and source azimuth is similar to a neural measure of auditory directionality (interaural latency). There were some differences between freely walking and tethered conditions, although both showed qualitatively similar responses. Flies accelerated more slowly and attained lower maximum velocities on the treadmill, consistent with the greater inertia of the treadmill sphere relative to the flies. Also, flies tended to continue walking longer on the treadmill following cessation of the stimulus.</p>
1 aMason, A., C.1 aLee, Norman1 aOshinsky, Michael, L.  uhttp://jeb.biologists.org/cgi/doi/10.1242/jeb.0192602217nas a2200169   4500008004100000245007100041210006900112520157100181653001401752653002401766653002401790653001501814653002201829653001601851100002601867856015401893       2002                        eng d00aPhysiology of the Auditory Afferents in an Acoustic Parasitoid Fly0 aPhysiology of the Auditory Afferents in an Acoustic Parasitoid F3 a<p>The fly, Ormia ochracea, possess a novel auditory organ, which allows it to detect airborne sounds. The mechanical coupling of its pair of tympanal membranes provides the basis for a unique means of sensing the direction of a sound source. In this study, we characterized the neuroanatomy, frequency tuning, and neurophysiological response properties of the acoustic afferents. Our experiments demonstrate that the fly&#39;s nervous system is able to encode and localize the direction of a sound source, although the binaural auditory cues available in the acoustic sound field are miniscule. Almost all of the acoustic afferents recorded in this study responded to short and long sound pulses with a phasic burst of one to four action potentials. A few afferents responded tonically for the duration of the sound stimulus. A prominent class of afferents responds to suprathreshold stimuli with only a single spike discharge, independent of stimulus level, frequency, or duration. We also tested the response of the afferents to speakers separated by 180&deg; along the azimuth of the fly. We found that the afferent responses have a shorter latency because of ipsilateral stimulation. This could be a temporal code of the direction of a sound source. The threshold frequency tuning for the afferents revealed a range of sensitivities to the frequency of the cricket host&#39;s calling song frequency. The difference in the number of afferents above threshold on either side of the animal is a population code, which can also be used for sound localization.</p>
10aarthropod10adirectional hearing10amechanical coupling10aparasitoid10apopulation coding10atime coding1 aOshinsky, Michael, L.  uhttp://www.jneurosci.org/lookup/doi/10.1523/JNEUROSCI.22-16-07254.2002https://syndication.highwire.org/content/doi/10.1523/JNEUROSCI.22-16-07254.2002