02214nas a2200229 4500008004100000022001400041245008800055210006900143260001600212300001600228490000800244520146400252653002101716653001801737653001201755653002501767653001901792100002101811700001501832700001701847856012001864 2008 eng d a0022-094900aComparing passive and active hearing: spectral analysis of transient sounds in bats0 aComparing passive and active hearing spectral analysis of transi cMar-06-2009 a1850 - 18580 v2113 a

n vision, colour constancy allows the evaluation of the colour of objects independent of the spectral composition of a light source. In the auditory system, comparable mechanisms have been described that allows the evaluation of the spectral shape of sounds independent of the spectral composition of ambient background sounds. For echolocating bats, the evaluation of spectral shape is vitally important both for the analysis of external sounds and the analysis of the echoes of self-generated sonar emissions. Here, we investigated how the echolocating bat Phyllostomus discolor evaluates the spectral shape of transient sounds both in passive hearing and in echolocation as a specialized mode of active hearing. Bats were trained to classify transients of different spectral shape as low- or highpass. We then assessed how the spectral shape of an ambient background noise influenced the spontaneous classification of the transients. In the passive-hearing condition, the bats spontaneously changed their classification boundary depending on the spectral shape of the background. In the echo-acoustic condition, the classification boundary did not change although the background- and spectral-shape manipulations were identical in the two conditions. These data show that auditory processing differs between passive and active hearing: echolocation represents an independent mode of active hearing with its own rules of auditory spectral analysis.

10abackground noise10acall analysis10ahearing10aperceptual constancy10aspectral shape1 aGoerlitz, H., R.1 aHubner, M.1 aWiegrebe, L. uhttp://jeb.biologists.org/cgi/doi/10.1242/jeb.017715https://syndication.highwire.org/content/doi/10.1242/jeb.01771501987nas a2200157 4500008004100000245010400041210006900145260001600214490000600230520146900236100001701705700002501722700001801747700001901765856004501784 2016 eng d00aLinking the sender to the receiver: vocal adjustments by bats to maintain signal detection in noise0 aLinking the sender to the receiver vocal adjustments by bats to  cJan-11-20160 v53 a

Short-term adjustments of signal characteristics allow animals to maintain reliable communication in noise. Noise-dependent vocal plasticity often involves simultaneous changes in multiple parameters. Here, we quanti ed for the  rst time the relative contributions of signal amplitude, duration,
and redundancy for improving signal detectability in noise. To this end, we used a combination of behavioural experiments on pale spear-nosed bats (Phyllostomus discolor) and signal detection models. In response to increasing noise levels, all bats raised the amplitude of their echolocation calls by 1.8–7.9 dB (the Lombard e ect). Bats also increased signal duration by 13%–85%, corresponding to an increase in detectability of 1.0–5.3 dB. Finally, in some noise conditions, bats increased signal redundancy by producing more call groups. Assuming optimal cognitive integration, this could result in a further detectability improvement by up to 4 dB. Our data show that while the main improvement in signal detectability was due to the Lombard e ect, increasing signal duration and redundancy can also contribute markedly to improving signal detectability. Overall, our  ndings demonstrate that
the observed adjustments of signal parameters in noise are matched to how these parameters are processed in the receiver’s sensory system, thereby facilitating signal transmission in  uctuating environments.

1 aLuo, Jinhong1 aGoerlitz, Holger, R.1 aBrumm, Henrik1 aWiegrebe, Lutz uhttp://www.nature.com/articles/srep18556