Vibratory sources as compound stimuli for the octavolateralis systems: dissection of specific stimulation channels using multiple behavioral approaches

Abstract

Underwater vibratory sources simultaneously present acoustic and hydrodynamic disturbances. Because vibratory dipole sources are poor sonic projectors, most researchers have assumed that such sources are of greatest relevance to the lateral line system. Both hydroacoustic principles and empirical studies have shown that dipole sources are also a potent stimulus to the inner ear. Responses to vibratory sources in mottled sculpin (Cottus bairdi) were assessed using unconditioned orienting, differential and nondifferential conditioning. Orienting responses are dominated by lateral line inputs and eliminated by lateral line inactivation. Simple conditioning depends on inputs from other systems and was not affected by lateral line inactivation. Differential conditioning alters behavioral control, and sculpin could be conditioned to ignore substrate-borne vibrations and respond only to hydroacoustic stimulation of the ear. The lateral line and inner ear of mottled sculpin do not necessarily exhibit range fractionation, as both systems operate over a similar distance (within 1.5 body lengths) and respond to many of the same sources. Vibratory dipole sources generate compound stimuli that simultaneously activate multiple octavolateralis systems, and sculpin make use of the channels differentially under different behavioral tasks.

Figure 1

Schematic representation of the behavioral arenas used in these experiments. The subject (Fish) was either lured to the position indicated (experiment 1) or confined there in a tent-shaped cage (experiments two and three) and the stimulus was positioned along a transect perpendicular to the long axis of the fish. Source vibrations were parallel to the fish’s long axis. The position of recording and stimulating electrodes (experiments 2 and 3) are also shown as connected to the differential amplifier and the variable transformer respectively.

Figure 2

Schematic diagram of the behavioral measure used in experiment 1. The vertically oriented fish outline shows the initial starting position of the subject relative to the source (black circle, with vibration axis indicated by arrows). The second fish outline shows the position of the fish after the initial orienting turn to the vibrating bead. The new angle to the source (θ) is the orienting error.

Figure 3

Probability densities of all response possibilities in experiment 1. The probability of responses to blank trials is shown under the dashed line and the probability of any given response to a signal trial is shown under the solid lines. Each panel represents all responses to stimuli at a given distance, as indicated in the upper left corner of each graph. Note that the x-axis is ploted in descending values, to position higher confidence ratings (less orienting error after the first turn) to the right.

Figure 4

Receiver operating characteristic curves for each stimulus distance in experiment 1.

Figure 5

Detectability curves based on the ROC analyses for all three experiments. The horizontal dashed line represents a minimal level of detectability (p(A) = 0.76).

Figure 6

Measures of respiratory suppression from three trials during a training session. The first five seconds of respiration is shown under the heading prestimulus. The CS is delivered during the second five seconds of the trial and is immediately followed by the UCS (arrows). The relative amplitude of respiration during the second five seconds is represented as a suppression ratio (SR) of the respiration during the stimulus (stim) to the five seconds prior to the CS (pre) plus the respiration during the stimulus.

Figure 7

Probability densities of all response possibilities for all subjects in Experiment 2 (trained without differential conditioning). The probability of responses to blank trials is shown under the dashed line and the probability of any given response to a signal trial is shown under the solid lines. Each panel represents all responses to stimuli at a given distance, as indicated in the upper left corner of each graph.

Figure 8

ROC curves for response probabilities for each stimulus distance (symbols) in experiment 2.

Figure 9

(A) Schematic representation of the presentation schedule in experiment 3. A train of source vibrations (Pulse Train) is shown as a grey box. The bead travel is shown schematically reading from left to right. The bead begins in the water and is raised and lowered several times between trials. The two types of control experiments (Bead Out Control and Bead In Control) are also shown. (B) Response probabilities during these conditions is compared, using the Bead Out Control as a “signal” and the Bead In control as a non-signal condition to generate the ROC curve shown in C.

Figure 10

Probability densities of the responses of all subjects in experiment 3. The probability of responses to control trials (bead vibrating out of the water) is shown under the dashed line and the probability of any given response to a signal trial is shown under the solid lines. Each panel represents all responses to stimuli at a given distance, as indicated in the upper left corner of each graph.

Figure 11

ROC curves of all responses in experiment 3. Each stimulus distance is shown by different symbols.

Figure 12

Probability densities the responses of two subjects in experiment 3 following CoCl₂ inactivation of the lateral line system. The probability of responses to blank trials is shown under the dashed line and the probability of any given response to a signal trial is shown under the solid lines. Each panel represents all responses to stimuli at a given distance, as indicated in the upper left corner of each graph.

Figure 13

ROC curves for CoCl2 inactivated animals in experiment 3.

Figure 14

Schematic decision tree for evaluating multisensory interaction type. After Braun et al. 2002.