In the space below, describe what the combination-sensitive neurons in the bat brain respond to. Each of your answers should specify the key feature of a sound (frequency, time of arrival, or amplitude), the portion of the call that the sound is part of (CF or FM), which harmonics (1st/fundamental, 2nd or 3rd), whether the each sound is part of the call or part of the echo, and what information is encoded by the response of the combination-sensitive neurons. 1. (4.5 points) What does a combination-sensitive neuron in the CF-CF region respond to and what does it encode? 2. (4.5 points) What does a combination-sensitive neuron in the FM-FM region respond to and what does it encode? 3. (4 points) What does a combination-sensitive neuron in the DSCF region respond to and what does it encode?

 

What does a combination-sensitive neuron in the CF-CF region respond to and what does it encode?

• The CF/CF area contains neurons tuned to particular Doppler shifts, and the amount of Doppler shift is systematically expressed on the cortical surface. The CF/CF combination-sensitive neurons extract velocity information from paired CF components, and that the CF-CF responds poorly to single tones and single elements in the biosonar signal, but are facilitated by combinations of two signal elements. 

What does a combination-sensitive neuron in the FM-FM region respond to and what does it encode?

• The FM-FM area contains neurons tuned to particular echo delays that are systematically arrayed across the area. Just like the CF-CF region, FM-FM is also combination sensitive, in which this region responds poorly to single tones and single elements in the biosonar signal, but are facilitated by combinations of two signal elements. A feature of primary importance in the FM-FM region is the  regular mapping of an important information bearing parameter, that is, target range or velocity.

What does a combination-sensitive neuron in the DSCF region respond to and what does it encode?

• The Doppler-shifted CF (DSCF) processing area is the region containing the overrepresentation of the echo CF² in the auditory complex of the bat. The DSCF region occupies approximately 50% of the mustached bat's auditory complex. While flying, mustached bats lower the frequency of the emitted pulse to compensate for Doppler shifts in echoes, so that the DSCF, is stabilized to a frequency (called the reference frequency) that is typically between about 61 .O and 61.5 kHz. In addition, DSCF neurons are facilitated when the CF, is paired with frequencies contained in the first harmonic of the biosonar signal. DSCF neurons are suited to signal the presence of an insect within this behaviorally important range.