Bilateral capacity for speech sound processing in auditory comprehension: Evidence from Wada procedures

Abstract

Data from lesion studies suggests that the ability to perceive speech sounds, as measured by auditory comprehension tasks, is supported by temporal lobe systems in both the left and right hemisphere. For example, patients with left temporal lobe damage and auditory comprehension deficits (i.e., Wernicke's aphasics), nonetheless comprehend isolated words better than one would expect if their speech perception system had been largely destroyed (70-80% accuracy). Further, when comprehension fails in such patients their errors are more often semantically-based, thanphonemically based. The question addressed by the present study is whether this ability of the right hemisphere to process speech sounds is a result of plastic reorganization following chronic left hemisphere damage, or whether the ability exists in undamaged language systems. We sought to test these possibilities by studying auditory comprehension in acute left versus right hemisphere deactivation during Wada procedures. A series of 20 patients undergoing clinically indicated Wada procedures were asked to listen to an auditorily presented stimulus word, and then point to its matching picture on a card that contained the target picture, a semantic foil, a phonemic foil, and an unrelated foil. This task was performed under three conditions, baseline, during left carotid injection of sodium amytal, and during right carotid injection of sodium amytal. Overall, left hemisphere injection led to a significantly higher error rate than right hemisphere injection. However, consistent with lesion work, the majority (75%) of these errors were semantic in nature. These findings suggest that auditory comprehension deficits are predominantly semantic in nature, even following acute left hemisphere disruption. This, in turn, supports the hypothesis that the right hemisphere is capable of speech sound processing in the intact brain.

Wernicke’s area revisited: Parallel streams and word processing

“…The former assesses the stage prior to word-form recognition ( i.e ., phoneme recognition) while the latter assesses phrase comprehension, which includes semantic and syntactic processing. More refined methods (Miglioretti & Boatman, 2003; Hickok et al , 2008; Goll et al , 2010; Rogalski et al , 2011; Bormann & Weiller, 2012; Thothathiri, Kimberg & Schwartz, 2012) will be required in future investigations for the specific evaluation of auditory word-form recognition. It should be noted, however, that resection of sites implicated in auditory sentence comprehension by electrical interference does increase the incidence of post-operative impairment in auditory comprehension (Hamberger et al , 2005).…”

An fMRI study of perception and action in deaf signers

“…On one hand, there is ample evidence that the motor system activates during speech perception (Fadiga, Craighero, Buccino, & Rizzolatti, 2002; Hickok, Buchsbaum, Humphries, & Muftuler, 2003; Wilson, Saygin, Sereno, & Iacoboni, 2004) and that disruption of motor function can, in some cases, result in changes in performance on some tasks (D’Ausilio et al, 2009; Grossman et al, 2008; Meister et al, 2007; Mottonen & Watkins, 2009; Schomers, Kirilina, Weigand, Bajbouj, & Pulvermuller, 2014; Tranel, Kemmerer, Adolphs, Damasio, & Damasio, 2003). On the other hand, there is compelling evidence that the basic ability to perceive and understand speech is not substantially affected by chronic damage to motor speech systems (Hickok, Costanzo, Capasso, & Miceli, 2011; Rogalsky, Love, Driscoll, Anderson, & Hickok, 2011), acute and complete deactivation of motor speech ability (Hickok et al, 2008), or the failure to develop articulate speech (Bishop, Brown, & Robson, 1990). …”

Speech perception when the motor system is compromised

“…In a striking demonstration of redundancy in the brain regions supporting speech perception, Hickok and colleagues reported that in patients undergoing the Wada procedure, the right hemisphere alone made fewer than 10% phonemic errors[3]. This apparent redundancy limits the extent to which speech perception deficits can be observed when any single region, such as speech motor cortex, is damaged.…”