Comparison of Phonetic Convergence in Multiple Measures

During interaction, speakers acquire characteristics more similar to characteristics of their interlocutors’ speech and other behaviors; this is known as convergence.  In addition to non-linguistic characteristics such as posture (Dijksterhuis and Bargh 2001) and fidgeting movements (Chartrand and Bargh 1999), this has been found in many characteristics of speech, including pitch (Babel and Bulatov 2011), vowel formants (Babel 2012), intensity (Gregory and Hoyt 1982), lexical items (Ireland et al. 2011), syntactic constructions (Nilsenová and Noltig 2010), and timing of conversational turns and pauses (Street 1984).

A variety of explanations for convergence have been proposed.  The main explanations for linguistic convergence are understanding-based (e.g. Street and Giles 1982), socially motivated (e.g. Eckert 2001), or automatic (Dijksterhuis and Bargh 2001).  Each of these explanations has elements of support from a range of experiments.  As more studies add details to the range of influences on convergence and the characteristics affected by it, we can make a clearer picture of the cognitive representations of linguistic characteristics and their dynamics.

The amount of phonetic convergence between speakers has been associated with several factors, such as race (Babel 2012), gender (Pardo 2010), age (Labov 2006), nationality (Giles, Coupland, and Coupland 1991), native language (Kim et al. 2011), and interlocutor status (Gregory and Webster 1996, Bane et al. 2010/2014).  One large factor correlated with convergence is positiveness of interlocutors’ opinions of each other, using a range of positiveness measures.  Convergence occurs to a greater degree between people with positive relationships (Bernieri and Rosenthal 1991) and greater convergence leads to more positive opinions of interlocutors (Giles et al. 1973).  Convergence also depends on characteristics of the individuals involved: people who are more concerned with social status exhibit more convergence (Pardo 2006, Natale 1975).

However, the extent to which convergence in different characteristics aligns remains unclear; correlation between convergence in different measures has not been part of many previous studies, in part due to the different experimental designs suited to measuring different characteristics.  Convergence in word-level or phoneme-level characteristics such as vowel formants (e.g. Babel 2012) and voice onset time (e.g. Nielsen 2011) or in overall perceived similarity (e.g. Goldinger 1998) have often been featured in shadowing tasks, in which the participants were recorded repeating words immediately after hearing a recording of them (e.g. Goldinger 1998, Babel 2012) and in interactive tasks designed to elicit repetition of words or concepts (e.g. map task in Pardo 2006; mazes in Garrod and Doherty 1994).  Larger-scale patterns such as lexical choice, syntax, intensity, turn durations, and pause durations have often been measured in natural conversational settings (e.g. Gregory and Hoyt 1982, Natale 1975, Bernieri and Rosenthal 1991).

While convergence has been observed in each of these measures and some of them are independently correlated with some of the same social conditions, e.g. ratings of closeness and amount in common (Pardo 2012) and absolute measurements, e.g. number of turns and amount of overlapping speech (Levitan et al. 2012), it is not clear that convergence in each of these characteristics behaves the same way, because of the lack of correlation tests between measures.  The results of one recent study by Pardo et al. (2015) on F1, F2, and F0 suggest that the pattern of convergence can differ depending on which measure is used.  Degree of convergence based on perceptual testing of similarity has been correlated with the convergence exhibited in characteristics such as pitch and vowel duration (e.g. Pardo 2010), though in some studies researchers have not found correlation between the results of the perceptual test and the phonetic characteristic tested (e.g. Babel and Bulatov 2011, Pardo et al. 2012).

In this study, the relative patterns of convergence were investigated for eight different characteristics across pairs of interlocutors: F1, F2, vowel duration, F0, intensity, turn duration, duration of pauses marking the transition to a new speaker, and duration of pauses after which the same speaker resumed.  Convergence was calculated by comparing the average value in each measure for each participant over four time periods and then comparing the average difference between partners’ averages through those time periods.  After calculating convergence in each measure, the correlation between convergence in each possible combination of measures was analyzed, to determine how closely convergence in one measure aligns with convergence in other measures.  

I hypothesized that convergence in each measure would be positively correlated with the other measure, if the same mechanism underlies convergence in each of these measures; degree of convergence within a pair in vowel formants, F0, intensity, and timing of turns, turn-switching pauses, and within-turn pauses would be predictive of degree of convergence in each of the other measures. The null hypothesis was that convergence in each measure is not correlated with other measures; degree of convergence within a pair in vowel formants, F0, intensity, and timing of turns, turn-switching pauses, and within-turn pauses will not be predictive of degree of correlation in any other measure, suggesting that convergence is mediated through individual differences in attention to different acoustic and timing characteristics of speech, or that there is a slightly different process underlying convergence in different characteristics.  Either result has implications for experimental design in convergence research.