of the organizational effect of androgen. When T or 11-ketoT is implanted
into juvenile males (whether they will be type I or II cannot be distinguished at this stage), their sonic muscle becomes masculinized and resembles that of type I males. The treatment was ineffective in adult type II
males, suggesting that the peripheral differentiation takes place during
development and is irreversible in adulthood (Brantlly et al. 1993b). Thus,
a morph-specific profile of circulating androgen in adulthood does not
account for hypertrophy of sonic muscle in the plainfin midshipman fish.
Rather, exposure to T or 11-ketoT during development is likely to organize the sonic muscle in this species.
In the juvenile plainfin midshipman fish, the differential action of aromatase may account for the differentiation of the vocal pathways in the
CNS. In the vocal midbrain region, the aromatase activity of females and
type II males (nonsinging morph) was much higher than that in type I males
(singing morph), suggesting that aromatase may play a critical role in organizing the vocal circuitry of singing and nonsinging animals by converting
circulating androgen into estrogen.
5. Hormonal Basis of Acoustical Signal Perception
In comparison to hormonal control of vocal production, the endocrine basis
of acoustic perception has received less attention, perhaps because the
study of perception of animals at a behavioral level is quite difficult.
Acoustic perception of animals only becomes apparent when they express
behavioral responses to stimuli; signals perceived without an overt behavioral response cannot be distinguished from signals that are not perceived.
Thus, slight modulations in perception that might result from changes in
hormonal state often are not observable.
Two techniques are commonly used to study acoustic perception: playback experiments and operant conditioning. Playbacks involve presentation
of prerecorded or synthesized acoustic stimuli to animals and observation
of their behavioral responses (e.g., phonotaxis, copulation postures). When
animals respond differently to acoustic stimuli, one can deduce that the
stimuli were perceived differently by the animal. When animals reliably
show stereotyped behavioral responses to particular auditory stimuli, this
technique can be a powerful tool in understanding their perception. When
naturally occurring behavioral responses are difficult to elicit, operant conditioning is often used. In this experimental paradigm, the animal is first
trained to respond to a sensory stimulus with a certain motor response (e.g.,
pecking a key in response to hearing a tone); later, the animal is presented
with a test stimulus to determine whether the conditioned response will be
elicited. If the animal fails to respond to a test stimulus, the training and
test stimuli are regarded as having been perceived differently.
6. Hormonal Control of Communication
307
into juvenile males (whether they will be type I or II cannot be distinguished at this stage), their sonic muscle becomes masculinized and resembles that of type I males. The treatment was ineffective in adult type II
males, suggesting that the peripheral differentiation takes place during
development and is irreversible in adulthood (Brantlly et al. 1993b). Thus,
a morph-specific profile of circulating androgen in adulthood does not
account for hypertrophy of sonic muscle in the plainfin midshipman fish.
Rather, exposure to T or 11-ketoT during development is likely to organize the sonic muscle in this species.
In the juvenile plainfin midshipman fish, the differential action of aromatase may account for the differentiation of the vocal pathways in the
CNS. In the vocal midbrain region, the aromatase activity of females and
type II males (nonsinging morph) was much higher than that in type I males
(singing morph), suggesting that aromatase may play a critical role in organizing the vocal circuitry of singing and nonsinging animals by converting
circulating androgen into estrogen.
5. Hormonal Basis of Acoustical Signal Perception
In comparison to hormonal control of vocal production, the endocrine basis
of acoustic perception has received less attention, perhaps because the
study of perception of animals at a behavioral level is quite difficult.
Acoustic perception of animals only becomes apparent when they express
behavioral responses to stimuli; signals perceived without an overt behavioral response cannot be distinguished from signals that are not perceived.
Thus, slight modulations in perception that might result from changes in
hormonal state often are not observable.
Two techniques are commonly used to study acoustic perception: playback experiments and operant conditioning. Playbacks involve presentation
of prerecorded or synthesized acoustic stimuli to animals and observation
of their behavioral responses (e.g., phonotaxis, copulation postures). When
animals respond differently to acoustic stimuli, one can deduce that the
stimuli were perceived differently by the animal. When animals reliably
show stereotyped behavioral responses to particular auditory stimuli, this
technique can be a powerful tool in understanding their perception. When
naturally occurring behavioral responses are difficult to elicit, operant conditioning is often used. In this experimental paradigm, the animal is first
trained to respond to a sensory stimulus with a certain motor response (e.g.,
pecking a key in response to hearing a tone); later, the animal is presented
with a test stimulus to determine whether the conditioned response will be
elicited. If the animal fails to respond to a test stimulus, the training and
test stimuli are regarded as having been perceived differently.
6. Hormonal Control of Communication
307