| Abstract: | Using a habituation/dishabituation procedure, near-term foetuses (36-39 weeks gestational age) were tested in a low variability HR state, to examine whether they could discriminate between a male and a female voice repeatedly uttering the same short sentence. Prosody and loudness of the two voices were controlled. Once the foetal heart rate (HR) habituated to the first voice, the effect of a second voice was investigated in two experimental conditions: male/female voice and female/male voice. HR variations after the onset of the second voice were compared to those occurring in two control conditions in which the same voice was presented twice (male/female voice and female/female voice). Highly conservative statistical criteria taking each subject's pre-stimulus HR variability into account showed that most foetuses exposed to the voice change displayed decelerative cardiac changes, with no significant difference between the two conditions. These HR decelerations were found in the first seconds following the onset of the new voice, and reached their peak amplitude within 10 s in most subjects. These responses lasted more than 10 s for two-thirds of the experimental subjects. Mostly transient HR accelerations and only a few decelerative changes were recorded in the control subjects. Furthermore, mean amplitudes of these changes were significantly lower than the HR decelerations induced by the new voice in the experimental conditions, suggesting that the latter were not spontaneous HR modifications but rather cardiac responses to the voice change. It is argued that near-term foetuses may perceive a difference between voice characteristics of two speakers when they are highly contrasted for fundamental frequency and timbre. |
