Capacitance discrimination in electrolocating, weakly electric pulse fish (original) (raw)
Related papers
1993
Summary Weakly electric fish can perceive electric properties of objects by monitoring the responses of their epidermal electroreceptors (mormyromasts) to their own electric organ discharges (EOD), a process known as active electrolocation. Mormyrid fish can distinguish capacitative from resistive properties of objects. It is mainly animate objects that possess capacitative properties. Water conductivity is a critical environmental factor that varies
Journal of Comparative Physiology A, 1992
Gnathonemus petersii discriminates between ohmic and capacitive objects. To investigate the sensory basis of this discrimination we recorded from primary afferents that innervate either A or B mormyromast sensory cells. Modified and natural electric organ discharges were used as stimuli. In both A and B fibres frequencies below the peak-power frequency (3.8 to 4.5 kHz) of the electric organ discharge caused minimal first-spike latencies and a maximum number of spikes. A fibres did not discriminate phase-shifted stimuli, whereas B fibres responded significantly with a decrease in first-spike latency if the phase shift was only-1 ~ In both A and B fibres an amplitude increase caused a decrease in spike latency and an increase in spike number; an amplitude decrease had the reverse effect. If stimulated with quasi-natural electric organ discharges distorted by capacitive objects, the responses of A fibres decreased with increasing signal distortion. In contrast, the responses of B fibres increased until amplitude effects began to dominate. Gnathonemus may use the physiological differences between A and B fibres to detect and discriminate between capacitive and purely ohmic objects.
Journal of Comparative Physiology A, 1995
The "novelty response" of weakly electric mormyrids is a transient acceleration of the rate of electric organ discharges (EOD) elicited by a change in stimulus input. In this study, we used it as a tool to test whether Gnathonemus petersii can perceive minute waveform distortions of its EOD that are caused by capacitive objects, as would occur during electrolocation. Four predictions of a hypothesis concerning the mechanism of capacitance detection were tested and confirmed: (1) G. petersii exhibited a strong novelty response to computer-generated (synthetic) electric stimuli that mimic both the waveform and frequency shifts of the EOD caused by natural capacitive objects (Fig. 3). (2) Similar responses were elicited by synthetic stimuli in which only the waveform distortion due to phase shifting the EOD frequency components was present (Fig. 4). (3) Novelty responses could reliably be evoked by a constant amplitude phase shifted EOD that effects the entire body of the fish evenly, i.e., a phase difference across the body surface was lacking (Figs. 3, 4). (4) Local presentation of a phase-shifted EOD mimic that stimulated only a small number of electroreceptor organs at a single location was also effective in eliciting a behavioral response (Fig. 5). Our results indicate that waveform distortions due to phase shifts alone, i.e. independent of amplitude or frequency cues, are sufficient for the detection of capacitive, animate objects. Mormyrids perceive even minute waveform changes of their own EODs by centrally comparing the input of the two types of receptor cells within a single mormyromast electroreceptor organ. Thus, no comparison of differentially affected body
Discrimination of objects through electrolocation in the weakly electric fish, Gnathonemus petersii
Journal of Comparative Physiology A, 1990
Three weakly electric fish (Gnathonemus petersii) were force-choice trained in a two-alternative procedure to discriminate between objects differing in their electrical characteristics. The objects were carbon dipoles in plexiglass tubing (length 2.5 cm, diameter 0.6 cm). Their electrical characteristics could be changed by varying the impedance of an external circuit to which they were connected (Fig. 1). In one (the 'capacitance dipole') the resistance was very low (< 3 fl) and the capacitance variable. In the other (the 'resistance dipole') the resistance was variable and the capacitance low (< 50 pV). Capacitances from several hundred pF ('lower thresholds', Fig. 2) to several hundred nF ('upper thresholds', Fig. 3) could be discriminated from both insulators and good conductors. In all cases the rewardnegative stimulus was the capacitance dipole, which was avoided by all fish spontaneously. Thresholds were defined at 70% correct choices. The fish were then tested for their ability to discriminate between one object with a given capacitance and another with resistances varying from 3 [2 to 200 kf~. The capacitance dipole continued to be the negative stimulus throughout. All 3 fish avoided it in at least 80% of the trials at each stimulus combination (Fig. 4). This result suggests that Gnathonemus perceives the capacitance and the resistance of objects differentially. The effect of the dipole-objects as well as some natural objects on the local EOD was recorded differentially very close to the fish's skin (Fig. 5). The amplitude of the local EODs was affected by all types of objects as they approached the skin. However, the waveform was changed only by capacitance dipoles and some natural objects (Figs. 6 and 7). It appears that the fish perceive not only intensity changes in the local EOD but waveform deformations as well and can thus distinguish objects of different complex impedances.
Electroreception inG. carapo: detection of changes in waveform of the electrosensory signals
The Journal of Experimental Biology, 2003
Electric fish explore the near environment by processing sensory signals evoked by their own self-generated electric fields (Lissmann, 1951, 1958; Lissmann and Machin, 1958). These fields are generated by the activation of electric organs (EO), which transform the fish bodies into a distributed electrical source. The field created by the electric organ discharge (EOD) generates a spatio-temporal pattern of current density that stimulates electroreceptors distributed over the skin. This field constitutes the carrier for active electrolocation signals, resulting from its modulation by objects with impedances different from that of water. The difference between the basal pattern of transcutaneous current density and the pattern in the presence of an object constitutes the electrical image of the object on the skin. Behavioral experiments have shown that both African (Mormyriform) and American (Gymnotiform) electric fish can discriminate objects on the basis of their capacitance (
Animal Behaviour, 1982
A characteristic electric organ discharge display in social encounters between mormyrid fish is a temporary discharge cessation. Using this response, we have investigated the useful range of electrocommunication under different water conductivity conditions in the mormyrid Brienomyrus niger. An individual fish was confined to a porous ceramic shelter tube and moved from a starting distance of 380 cm toward a similarly confined conspecific until discharge cessation occurred. The moved fish was subsequently returned to its original position. Water conductivity affects the peak-to-peak source voltage of the electric organ and the sensitivity of the fish's electroreceptors. Within a range of t0 to 36 000 gS/cm, the peak-to-peak amplitude of the electric organ discharge declined as a power function. At 120 pS/cm, the amplitude was 50%, and at 300 gS/cm, 30 ~ of the 10 pS/cm value. The interfish distance at which discharge cessation occurred and the associated electric field gradients were dependent on water conductivity and upon the spatial orientation of the two fish (end-to-end or parallel orientations of their shelter tubes). The respective ranges were from 135 cm and 0.02 mV/cm at 52 gS/cm (parallel orientation) to 22 cm and 0.36 mV/cm at 678 gS/cm (end-to-end orientation). When the data for both tube orientations were combined, the relationship between water conductivity (x) and the distance at which discharge cessation occurred (y) could be expressed by a power function, y = K. x" (with K = 10z.97 and a =-0.56). When an electrically 'silent' fish was moved away from its conspecific, a discharge resumption in the form of a high-frequency rebound occasionally effected changes in the other fish's discharge activity at distances up to 157 cm (with an associated electric field gradient of 0.01 mV/cm under the lowest conductivity condition).
Capacitance detection in the wave-type electric fish Eigenmannia during active electrolocation
Journal of Comparative Physiology A: Sensory, Neural, and Behavioral Physiology, 1998
Weakly electric ®sh can detect nearby objects and analyse their electric properties during active electrolocation. Four individuals of the South American gymnotiform ®sh Eigenmannia sp., which emits a continuous wave-type electric signal, were tested for their ability to detect capacitive properties of objects and discriminate them from resistive properties. For individual ®sh, capacitive values of objects had to be greater than 0.22±1.7 nF (`lower threshold') and smaller than 120±680 nF (`upper threshold') in order to be detected. The capacitive values of natural objects fall well within this detection range. All ®sh trained could discriminate unequivocally between capacitive and resistive object properties. Thus, ®sh perceive capacitive properties as a separate object quality. The eects of dierent types of objects on the locally occurring electric signals which stimulate electroreceptors during electrolocation were examined. Purely resistive objects altered mainly local electric organ discharge (EOD) amplitude, but capacitive objects with values between about 0.5 and 600 nF changed the timing of certain EOD parameters (phaseshift) and EOD waveform. A mechanism for capacitance detection in wave-type electric ®sh based on time measurements is proposed and compared with the capacitance detection mechanism in mormyrid pulse-type ®sh, which is based on waveform measurements. Key words Weakly electric ®sh á Electrolocation Phase-shift á Time coding á Waveform Abbreviations EOD electric organ discharge p-p peak-to-peak á Eig 1 etc. Eigenmannia 1 etc.