Auditory processing and physiological factors T

Dichotic listening

enhance fluency for at least some people who stutter
enhance fluency for at least some people who stutter

Dichotic listening

Just as most school age children and adults have a hand preference, foot preference, and so on, so we too have an ear preference when it comes to auditory information. One way to test this preference is by having different sounds played through headphones to the left and right ears simultaneously and noting which sound is perceived most readily. This procedure is called dichotic listening. However, just as handedness may be different for different tasks (for example, writing right-handedly and playing golf left-handedly), so too ear preference depends on the nature of the auditory signal. Most right-handed and right-sided adults who do not stutter will more accurately report musical stimuli when it is presented to the left ear, while there is a slight bias towards the right ear for linguistically meaningful information (Kimura, 1963, 1967). Note that due to the decussation (crossing) of the neural path-ways involved, a right ear preference indicates left hemisphere dominance and vice versa. This pattern of auditory preference reflects the notion that musical encoding and decoding takes place in the right hemisphere, and lin-guistic processing takes place in the left in right-sided adults who do not stutter. In saying this, though, we must also acknowledge the complexities we noted in chapter 2 when attempting to link peripheral events, such as handedness, to hemispheric lateralization
As seems to be the case with hemispheric processing for speech and lan-guage (that is, relating to production aspects of communication), there is evidence that there are similar processing differences between the preferences of those who do and do not stutter with regard to auditory perception. Curry
52 Stuttering and clutteringand Gregory (1967) found that a group of 20 adults who stuttered showed a significantly reduced right ear preference to dichotically presented common consonant vowel consonant (CVC) words over their matched nonstuttering control group. Quinn (1972) attempted a replication of this research with a larger cohort of subjects (60), and although no significant differences were found, subsequently realized that some of the supposed right-handed people who stutter actually used their left hands for some tasks (for example, a number reportedly played golf left-handed). Rosenfield and Jerger (1984) suggested that this might be a confounding factor in this and other studies and it remains a point of contention today. As we see in chapter 2, there is good evidence that only a very few people are strongly right dominated, and even within the domain of handedness, there are many who switch hands for certain tasks, even if they use their right hand to write. In a more robustly designed experiment, Rosenfield and Goodglass (1980) found that a group of people who stutter showed a right ear preference for linguistic consonant-vowel (CV) stimuli and a left ear preference for melodic stimuli, and that there were no significant differences between this group and a matched group of people who did not stutter. Despite this, a significantly larger proportion of the people who stutter group failed to demonstrate the expected pattern of dominance of either linguistic or melodic stimuli than the control group.
What does seem consistent is that when the stimulus becomes less linguistic-ally relevant, the less obvious is the ear preference difference between experi-mental and control groups. For example, neither Slorach and Noehr (1973) nor Gruber and Powell (1974) found any significant difference between children who stutter and control groups when digit pairs were presented dichotically. A similar effect has been noted when meaningless CV structures have been used (Dorman & Porter, 1975). It is likely, of course, that younger preschool children may have less complete lateralization than older children and adults
An interesting variation of the dichotic listening paradigm was developed by Sussman and MacNeilage (1975) who asked people who stutter to control the pitch of a tone presented in one ear to match the pitch of a tone presented to the other ear by moving the tongue and jaw up and down accordingly. A right ear advantage was noted for both this group, and a group of matched control speakers. However, the control group, expectedly, were better able to use their tongues to manipulate the tone when the tone that responded to tongue height was presented to the right ear, whereas the group of people who stutter showed a left ear preference for that tone; apparently demonstrat-ing a difficulty with motor and sensory integration rather than with an audi-tory problem alone. A later replication of the auditory tracking experiment (Neilson, Quinn, & Neilson 1976) found a similar finding for nonstuttering speakers, but no significant difference between this group and a group of adults who stuttered

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