RESUMEN
The effects of signal onset/offset envelope on the underwater hearing thresholds of a harbor seal (Phoca vitulina) were measured. Pure-tone, 540-ms pulses at 2, 4, 8, and 16 kHz were presented as test signals. An ANOVA revealed that there were no significant differences between repeated threshold measures for abrupt onset/offset signal envelopes versus slow onset/offset signal envelopes [F = 4.380, d.f. = (1,18), p > 0.05]. Seal vocalizations which have an abrupt onset/offset may be serving a short-range communicative function by helping the listener determine the direction of a nearby sender.
Asunto(s)
Umbral Auditivo , Phocidae/fisiología , Detección de Señal Psicológica , Animales , Diseño de Equipo , Audición/fisiología , MasculinoRESUMEN
Many seal vocalizations consist of frequency swept tones. The signal detection thresholds of a harbor seal (Phoca vitulina) and of human listeners were measured using ascending and descending frequency swept tones at 1/3- and 1-oct bandwidths. The swept tones increased or decreased exponentially and traversed the same frequency range. The sweeps were centered on 2, 4, and 8 kHz for the seal study and 0.5, 1, and 2 kHz for the human listeners. The bandwidth of the sweep did not affect signal detection abilities of either the seal or human listeners. The seal had lower signal detection thresholds (1-5 dB) when presented with the descending frequency swept tones (F = 32.04, df = (1,31), p < 0.000001). Human listeners also had lower detection thresholds for descending frequency swept tones (t = -4.78, df = 52, p < 0.0001). Pinniped ascending frequency swept calls may not function as well as descending frequency sweeps for long-distance communicative signals.
Asunto(s)
Percepción Auditiva , Umbral Auditivo , Phocidae , Detección de Señal Psicológica , Adulto , Animales , Femenino , Humanos , Masculino , Persona de Mediana Edad , RuidoRESUMEN
Threshold changes associated with separating a signal source and a masking white noise source from 0 degree to 90 degrees were determined for 0.5, 1 and 8 kHz pure tones and click trains. No changes occurred for the 0.5 and 1 kHz pure tones. Masked thresholds of 8 kHz pure tones and click trains decreased linearly by 9 and 13 dB respectively as angular separation was moved from 0 degree to 90 degrees. Changes in click train stimuli masked thresholds did not change significantly when the ear directed toward the masking source was occluded (11 dB drop at 90 degrees). The absence of changes at low frequencies and the similarity in magnitude of the changes in signals containing high frequency components with the responses to the monaural click trains, suggests that the threshold changes can be attributed to a head shadow effect. The casting of a sound shadow effectively lowers the noise level on the shielded side. These findings question the importance of cross-correlation techniques when detecting signals in noise.