Perceptual complexity of lexical, surface structure, and deep structure types of ambiguous sentences and change in heart rate.

Studies comparing lexical, surface-, and deep-structure types of ambiguous sentences with unambiguous ones for perceptual complexity show conflicting findings mainly because of task artifacts and lack of adequate control of confounding variables. In the present study, three types of ambiguous sentences and matched unambiguous controls were compared. Acceleration and deceleration measures of heart rate (HR) were used since these have been shown to reliably indicate complexity of cognitive activity. The study used a Groups x Ambiguity Condition x Ambiguous Sentence-Type x Sentence-Clusters repeated measures Latin Square ANOVA design which permitted isolation of variance related to the specific sample of sentences used. Eighteen low-bias ambiguous sentences (six from each type) and their control pairs, divided into three lists, were presented to 30 male undergraduates. Analysis of data showed: (1) significant Ambiguity x Type and Ambiguity effects for the percentage of increase in HR during processing of the sentence and, (2) significant effect of Ambiguity for the percentage of decrease in HR. These results were interpreted as showing that while low-bias ambiguous sentences are perceptually more complex than unambiguous ones, the effect of ambiguity may be greater for deep-structure type of ambiguous sentences than for lexical and surface-structure types.