Angular range, not velocity, dominates barn owl auditory motion discrimination sensitivity

Evidence

For any trial the starting point, motion direction, velocity (53–2400°/s), duration (30–225 ms) and angular range (12–72°) of the noise sweeps were randomized. Each test stimulus had a motion direction being opposite to that of the reference stimuli. Stimuli were presented in the frontal or the lateral auditory space. … The angular extent of the motion had a large effect on the owl’s discrimination sensitivity allowing a better discrimination for a larger angular range of the motion. In contrast, stimulus velocity or stimulus duration had a smaller, although significant effect. — Dijk, Pim van, Physiology, Psychoacoustics and…, 3178

Our behavioural data obtained with noise sweeps in the free field and with an angular velocity between 53 and 2400°/s are in accord with the observed broad angular velocity tuning. Stimulus velocity had a moderate effect on motion direction sensitivity provided that the stimulus duration was not too short. Duration of the noise sweeps per se had only a moderate effect on the behavioural sensitivity. Sensitivity was lower for short than for long stimulus durations. We could observe the lowest sensitivity for stimuli of 30 ms duration. This result is in accord with data describing the barn owl’s binaural temporal window for ITD processing ranging from 4 to 42 ms (Wagner 1991 ). Inhibitory neuronal processing has been observed to be effective already between 20 and 40 ms after stimulus onset (Wagner 1990 ). Inhibition could thus contribute to the dynamic sharpening of the ITD representation in the barn owl’s IC and to the duration of the binaural temporal window. — Dijk, Pim van, Physiology, Psychoacoustics and…, 3216

Motion direction sensitive neurons have been observed in the barn owl IC and optic tectum (Wagner et al. 1997 , Wagner and von Campenhausen 2002 ). Neurophysiological studies on directional sensitivity in auditory motion processing by the owl have applied a wide range of angular velocities. Witten et al. ( 2006 ) presented simulated motion based on ITD change at a speed of 32°/s observing shifts of auditory spatial receptive fields in relation to motion direction that could be explained by adaptation. Similarly, Wang and Peña ( 2013 ) showed that adaptation affected direction selectivity for simulated motion of 470°/s in free-field stimulation. Wagner and Takahashi ( 1992 ) observed a broad tuning of motion direction selective units with respect to stimulus velocity when presenting simulated motion with an angular velocity ranging between 125 and 1200°/s. They suggest that inhibition accounts for the directional sensitivity. Our behavioural data obtained with noise sweeps in the free field and with an angular velocity between 53 and 2400°/s are in accord with the observed broad angular velocity tuning. Stimulus velocity had a moderate effect on motion direction sensitivity provided that the stimulus duration was not too short. — Dijk, Pim van, Physiology, Psychoacoustics and…, 3218

Here we report auditory motion perception in the barn owl, a species for which data on the neuronal representation of motion stimuli in the inferior colliculus (IC) are available (e.g., Wagner and Takahashi 1992 ; Kautz and Wagner 1998 ; Wagner and von Campenhausen 2002 ; Wang and Peña 2013 ). Specifically, Wagner and Takahashi ( 1992 ) showed that the angular velocity and stimulus duration affected the neurons’ response. Here, we investigate how stimulus velocity, the size of the angle of sound incidence (i.e., the angular range), and stimulus duration affect the owls’ perceptual performance. Furthermore, we analyse whether the perception of changes in motion direction differs for stimuli presented in the frontal or in the lateral space. — Dijk, Pim van, Physiology, Psychoacoustics and…, 3185

Our data show that the owls’ sensitivity for auditory motion discrimination mainly increased with increasing angular range. The amount of variance accounted for (R2 ) by “angular range” was between 0.70 and 0.80 for each of the conditions shown in Figs. 2 and 3 . Stimulus duration and stimulus velocity had only a small, though significant effect on sensitivity. When comparing sensitivity at similar angular ranges, sensitivity moderately increased for longer stimuli and decreased for faster moving stimuli (R2 values for “duration” were between 0.03 and 0.13, R2 values for “velocity” were between 0.07 and 0.21, all P ≤ 0.001). — Dijk, Pim van, Physiology, Psychoacoustics and…, 3181

Our data show that the owls’ sensitivity for auditory motion discrimination mainly increased with increasing angular range. The amount of variance accounted for (R2 ) by “angular range” was between 0.70 and 0.80 for each of the conditions shown in Figs. 2 and 3 . Stimulus duration and stimulus velocity had only a small, though significant effect on sensitivity. When comparing sensitivity at similar angular ranges, sensitivity moderately increased for longer stimuli and decreased for faster moving stimuli (R2 values for “duration” were between 0.03 and 0.13, R2 values for “velocity” were between 0.07 and 0.21, all P ≤ 0.001). The same pattern was represented by the ANOVA results: the factor “angular range” had F-values of at least 854, F-values for “duration” were between 12 and 55, F-values for “velocity” were between 25 and 95 (all P ≤ 0.001). — Dijk, Pim van, Physiology, Psychoacoustics and…, 3197

Categorization

• XREF: Connects to the wider psychophysical principle of integration time windows in auditory processing, similar to how human minimum audible movement angle depends on stimulus duration. — connects to: Barn owls can be trained to report acoustic motion direction changes — Dijk, Pim van, Physiology, Psychoacoustics and…, 3178; Inhibition and adaptation, not velocity matching, drive motion direction selectivity; Frontal space yields better auditory motion discrimination than lateral space (+5 more)
• QUESTION: Is the 30ms degradation evidence of the inhibitory circuit’s developmental window, or of a different temporal-integration mechanism entirely?
• corroborated: 8 independent passages support this claim — Dijk, Pim van, Physiology, Psychoacoustics and…, 3178; Dijk, Pim van, Physiology, Psychoacoustics and…, 3216; Dijk, Pim van, Physiology, Psychoacoustics and…, 3218 (+3 more)

Broader Connections

• Barn owls judge sound direction via dedicated motion circuits, not endpoint comparison. #corroborates (0.90)
• Auditory motion perception is not computed from endpoint comparisons #corroborates (0.90)
• The minimum audible angle quantifies the just-detectable change in sound source position #expands (0.80)
• Short-duration motion stimuli exceed the owl’s binaural temporal integration window #expands (0.75)