A primer on dichotic listening as a paradigm for the assessment of hemispheric asymmetry

Figures & data

Figure 1. Waveforms for the syllables /ba/ and /pa/ as used in dichotic listening aligned between channels (L, left; R, right) to the onset of the “burst” of the consonant (C). V₁ and V₂ mark the approximate onset of the vowel in both syllables. The short interval between C and V₁ for /ba/ (i.e., the short voice-onset time), is characteristic for voiced syllables. The relative longer voice-onset time, C to V₂, for /pa/ is characteristic for an unvoiced syllable. Onset alignment with comparable vowel length leads (a) to offset differences between syllables and (b) to a reduced spectro-temporal overlap between mixed-voicing pairs, like /ba/ and /pa/.

Figure 2. Reliability as a function of trial number in free-report dichotic-listening paradigm using (non-word) CV syllables. Orange line: empirical reliability estimates as reported by Speaks et al. (1982). Blue line: average empirical reliability across different studies (for 30 trial paradigm from Hugdahl & Hammar, 1997, for 60 trials from Bryden, 1975; Shankweiler & Studdert-Kennedy, 1975; Van der Haegen & Brysbaert, 2018, and for 120 trials from Springer & Searleman, 1978; Wexler et al., 1981). Black line: estimated reliability calculated using the Spearman-Brown formula based on the empirical reliability of .61 reported for 20 trials by (Hugdahl & Hammar, 1997). All three plots indicate reliability >.80 at 120 trials.

Figure 3. Effect of stimulus repetition in dichotic listening on the BOLD response. Results from an fMRI study on N = 113 subjects (age: 29.3 ± 7.1 years; 49 females) using sCV syllables as stimulus material. Stronger activation in trials which did not contain a repeated stimulus (non-rep), as compared to trials which repeated a stimulus from a preceding trial (rep). Significant activation differences were found bilaterally in superior temporal gyrus (stg) and planum temporale (pt), as well as in the right Heschl’s gyrus (hg). Family-wise error correction (FWE) to p = .05 and a cluster threshold of 10 voxels were applied. Reported in Westerhausen et al. (2014b); reanalysed data from Kompus et al. (2012).

Table 1. Five design principles for a reliable dichotic-listening paradigm, measures how to adhere to these principles, and benefits achieved.

	Principle	Measures	Benefit
1	Keep it simple	Single stimulus pair per trial, single response, immediate response collection, free-recall instruction	Minimizes working-memory load and the demand for cognitive-control process
2	Maximize the spectral and temporal overlap of the paired stimuli	Use rhyming stimuli, assure inter-channel onset synchronization	Increases likelihood of perceptual fusion, reducing the cognitive demands of the paradigm
3	Equalize perceptual difficulty of the paired stimuli	Comparable stimulus difficulty and perceptual saliency, control for negative priming between trials, present all stimuli equally often to the left and the right ear	Prevents or controls for processing biases favouring one ear or the other stimulus.
4	Ensure fair testing conditions	Hearing acuity testing, good testing environment, language appropriateness	Minimizes the likelihood that factors other than perceptual laterality affect the measures
5	Collect a sufficient amount of responses	Use a minimum number of 90 (dichotic) trials, preferably 120	Improves ratio of effect variance to random error variance.

Speaks, C., Niccum, N., & Carney, E. (1982). Statistical properties of responses to dichotic listening with CV nonsense syllables. The Journal of the Acoustical Society of America, 72(4), 1185–1194.

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