Examining the phonological neighborhood density effect using near infrared spectroscopy

Abstract

Phonological density refers to the number of words that can be generated by replacing a phoneme in a target word with another phoneme in the same position. Although the precise nature of the phonological neighborhood density effect is not firmly established, many behavioral psycholinguistic studies have shown that visual recognition of individual words is influenced by the number and type of neighbors the words have. This study explored neurobehavioral correlates of phonological neighborhood density in skilled readers of English using near infrared spectroscopy. On the basis of a lexical decision task, our findings showed that words with many phonological neighbors (e.g., FRUIT) were recognized more slowly than words with few phonological neighbors (e.g., PROOF), and that words with many neighbors elicited significantly greater changes in blood oxygenation in the left than in the right hemisphere of the brain, specifically in the areas BA 22/39/40. In previous studies these brain areas have been implicated in fine-grained phonological processing in readers of English. The present findings provide the first demonstration that areas BA 22/39/40 are also sensitive to phonological density effects.

Figure 1

Positions of the probes used. Open circles denote laser emitters and filled circles denote laser detectors. Two laser emitters were placed at TP₃ and TP₄ following International 10/20 system. The distances between laser emitters and detectors were set at 3 cm.

Figure 2

Grand average changes of the concentration in oxy‐hemoglobin in (a) left hemisphere and in (b) right hemisphere. The data were analyzed in 17‐second epochs with 2 seconds before and 15 seconds after the onset of the stimuli. Black lines represent data for words with high phonological neighborhood density and gray lines represent data for words with low phonological neighborhood density. Circles on the black lines indicate time points at which the changes in blood oxygenation were significantly different from zero for words with high phonological neighborhood density. Circles on the gray lines indicate time points at which the changes in blood oxygenation were significantly different from zero for words with low phonological neighborhood density. The bars on each time point show the standard errors. The asterisks above and below the standard error bars indicate time points at which the changes in blood oxygenation were significantly different between words with high vs. low phonological neighborhood density. These analyses were controlled by the Bonferroni test for family‐wise error rate.

Figure 3

Grand average changes of the concentration in oxy‐hemoglobin in both left (LH) and right (RH) hemispheres for nonwords.

Figure 4

Grand average changes of the concentration in oxy‐hemoglobin (HBO₂) and deoxy‐hemoglobin (HBR) in both left (LH) and right (RH) hemispheres for two representative participants.