312
W.E Dolphin
unclear, although one possibility may be the differences in recording conditions. In contrast to Dolphin and colleagus, Supin and Popov obtained
responses from animals that remained at surface with the melon and
recording electrodes above water. Additionally, a single active electrode
was used by Supin and Popov as compared to the three electrode differential recording technique used by Dolphin's group.
The cutoff frequency from the MTFs above (3.0 to 305kHz) correspond
to a temporal integration time of roughly 300IlS. Although MTFs using
behavioral techniques have not been obtained from any cetacean, temporal resolution has been measured in terms of integration time, which has
been shown to be approximately 300llS (e.g., Au et al. 1988; Dubrovskiy
1990). It is possible to directly compare the MTF bandwidth to temporal
integration time using a Fourier transformation. The temporal integration
function may be converted to an equivalent rectangular duration (ERD)
and the MTF by an equivalent rectangular bandwidth (ERB). The frequency spectrum of a rectangular temporal function is
P(f) = [(sin(1tft))j1tf~]2
where P(f) is the spectral power,fis frequency, and ~ is ERD. The ERB of
this spectrum is
1
where closely to the results of studies such as that by Plack and Moore (1990). The
1,700Hz bandwidth obtained from the MTF in T truncatus yields an ERD
of 300lls, which agrees with the results from behavioral studies with this
species.
3.1.2.5 Multienvelope Stimuli
The modulation rate transfer functions obtained in the above-reported
studies demonstrate the ability of the cetacean auditory system to extract
and follow the envelope of a stimulus consisting of a single envelope component. A more natural situation, however, is one in which the acoustic
waveform impinging on the listener is highly complex, often consisting
of multiple envelope components. Communication calls of most species
contain multiple envelope frequencies, and in echolocation tasks, although
the emitted echolocating signal consists of a brief (microsecond duration)
broadband pulse or click having a relatively simple temporal structure, the
returned echo is likely to be several milliseconds in duration and highly
amplitude modulated (e.g., Au et al. 1988). A signal's amplitude-time variation, or envelope, contains nonspectral information that can be used by
W.E Dolphin
unclear, although one possibility may be the differences in recording conditions. In contrast to Dolphin and colleagus, Supin and Popov obtained
responses from animals that remained at surface with the melon and
recording electrodes above water. Additionally, a single active electrode
was used by Supin and Popov as compared to the three electrode differential recording technique used by Dolphin's group.
The cutoff frequency from the MTFs above (3.0 to 305kHz) correspond
to a temporal integration time of roughly 300IlS. Although MTFs using
behavioral techniques have not been obtained from any cetacean, temporal resolution has been measured in terms of integration time, which has
been shown to be approximately 300llS (e.g., Au et al. 1988; Dubrovskiy
1990). It is possible to directly compare the MTF bandwidth to temporal
integration time using a Fourier transformation. The temporal integration
function may be converted to an equivalent rectangular duration (ERD)
and the MTF by an equivalent rectangular bandwidth (ERB). The frequency spectrum of a rectangular temporal function is
P(f) = [(sin(1tft))j1tf~]2
where P(f) is the spectral power,fis frequency, and ~ is ERD. The ERB of
this spectrum is
1
where closely to the results of studies such as that by Plack and Moore (1990). The
1,700Hz bandwidth obtained from the MTF in T truncatus yields an ERD
of 300lls, which agrees with the results from behavioral studies with this
species.
3.1.2.5 Multienvelope Stimuli
The modulation rate transfer functions obtained in the above-reported
studies demonstrate the ability of the cetacean auditory system to extract
and follow the envelope of a stimulus consisting of a single envelope component. A more natural situation, however, is one in which the acoustic
waveform impinging on the listener is highly complex, often consisting
of multiple envelope components. Communication calls of most species
contain multiple envelope frequencies, and in echolocation tasks, although
the emitted echolocating signal consists of a brief (microsecond duration)
broadband pulse or click having a relatively simple temporal structure, the
returned echo is likely to be several milliseconds in duration and highly
amplitude modulated (e.g., Au et al. 1988). A signal's amplitude-time variation, or envelope, contains nonspectral information that can be used by