Behavioral evidence of a dissociation between voice gender categorization and phoneme categorization using auditory morphed stimuli

Abstract

Both voice gender perception and speech perception rely on neuronal populations located in the peri-sylvian areas. However, whilst functional imaging studies suggest a left vs. right hemisphere and anterior vs. posterior dissociation between voice and speech categorization, psycholinguistic studies on talker variability suggest that these two processes share common mechanisms. In this study, we investigated the categorical perception of voice gender (male vs. female) and phonemes (/pa/ vs. /ta/) using the same stimulus continua generated by morphing. This allowed the investigation of behavioral differences while controlling acoustic characteristics, since the same stimuli were used in both tasks. Despite a higher acoustic dissimilarity between items during the phoneme categorization task (a male and female voice producing the same phonemes) than the gender task (the same person producing 2 phonemes), results showed that speech information is being processed much faster than voice information. In addition, f0 or timbre equalization did not affect RT, which disagrees with the classical psycholinguistic models in which voice information is stripped away or normalized to access phonetic content. Also, despite similar average response (percentages) and perceptual (d') curves, a reverse correlation analysis on acoustic features revealed that only the vowel formant frequencies distinguish stimuli in the gender task, whilst, as expected, the formant frequencies of the consonant distinguished stimuli in the phoneme task. The 2nd set of results thus also disagrees with models postulating that the same acoustic information is used for voice and speech. Altogether these results suggest that voice gender categorization and phoneme categorization are dissociated at an early stage on the basis of different enhanced acoustic features that are diagnostic to the task at hand.

Hemispheric association and dissociation of voice and speech information processing in stroke

“…Analyses of perceptual distances (d') between successive pairs of items along continua revealed that none of the patient groups had increased perceptual distances for ambiguous items (figure 3), contrary to healthy subjects as shown in (Pernet et al, 2014). This result indicates a generalized reduction in categorical boundaries following stroke.…”

“…Paradigm: The experiment was identical to (Pernet et al, 2014), except that only pitch equalized stimuli were used. Participants carried out with two 2 alternative forced choice identification tasks: voice gender (male vs. female) and phoneme (/pa/ vs. /ta/), and responded by button press on a keyboard.…”

“…In normal heathy participants, this is achieved very easily. Taking the data from (Pernet et al, 2014), 100% of controls (N=18, 9 males, 9 females) were unimpaired (figure 2). From the resulting classification in patients, the independence between the phoneme and gender categorization performance was tested for each group using a McNemar test with exact central probability (Fay, 2010).…”

“…Here we investigated categorical perception in each group and task by testing if d' values differed from 0 (bootstrap-t test with Bonferroni correction -Wilcox, 2012) for each pair of stimuli along the continuum, thus delineating a perceptual boundary. Finally, differences between gender and phoneme categorization performances were tested comparing global d' values within groups (percentile bootstrap of the difference with adjustment for multiple testing) and relative to the healthy participants from (Pernet et al, 2014) (mean difference between groups, with adjustment for multiple comparisons based on the maximum statisticsWilcox, 2012).…”

“…Each participant categorized sounds from pitch equalized morphed continua as being male-female or /pa/-/ta/ (Pernet, Belin, & Jones, 2014). Stimuli were the same in both tasks, and participants had therefore to discard talker specific or phoneme specific information depending on the task at M A N U S C R I P T A C C E P T E D ACCEPTED MANUSCRIPT 3 hand.…”