Linking Sight and Sound: fMRI Evidence of Primary Auditory Cortex Activation during Visual Word Recognition

Brain and Language 76, 340–350 (2001) doi:10.1006/brln.2000.2433, available online at http://www.idealibrary.com on

Linking Sight and Sound: fMRI Evidence of Primary Auditory Cortex Activation during Visual Word Recognition Frank Haist Georgia State University

Allen W. Song Department of Radiology, Emory University

Krista Wild Georgia State University

Tracy L. Faber and Carol A. Popp Department of Radiology, Emory University

and Robin D. Morris Georgia State University Published online February 15, 2001

We describe two studies that used repetition priming paradigms to investigate brain activity during the reading of single words. Functional magnetic resonance images were collected during a visual lexical decision task in which nonword stimuli were manipulated with regard to phonological properties and compared to genuine English words. We observed a region in left-hemisphere primary auditory cortex linked to a repetition priming effect. The priming effect activity was observed only for stimuli that sound like known words; moreover, this region was sensitive to strategic task differences. Thus, a brain region involved in the most basic aspects of auditory processing appears to be engaged in reading even when there is no environmental oral or auditory component.  2001 Academic Press Key Words: repetition priming; phonological processing; orthographic processing; neuropsychology; lexical decision; reading; functional neuroimaging; fMRI.

Reading allows communication across time and people and is considered to be a major achievement in the evolution of human civilization (Diamond, 1997). Because Frank Haist is now at San Diego Children’s Hospital Research Center and University of California, San Diego. We thank Patricia Davis for cooperation in MR scanning; Jon Trudeau for technical assistance; and Natacha Akshoomoff, Rebecca Brenden Bone, and an anonymous reviewer for comments on previous versions of the manuscript. This word was supported, in part, by grants from the National Institute of Child Health and Human Development (HD 30970 and HD 22614 [to Marta Kutas, University of California, San Diego]) and Research Program Enhancement, Research Initiation, Quality Improvement Fund grants from the Georgia State University Office of Research and Sponsored Programs. Correspondence and reprint requests should be addressed to Frank Haist, Children’s Hospital Research Center, Research on the Neuroscience of Autism Lab, 8110 La Jolla Shores Dr., Suite 201, La Jolla, CA 92037. E-mail: [email protected]. 340 0093-934X/01 $35.00 Copyright  2001 by Academic Press All rights of reproduction in any form reserved.

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reading is a solely human creation and ability and the result of a complex array of integrated cognitive linguistic processes, understanding the neural correlates of this ability and its subsystems has been a primary focus of cognitive neuroscience. The ultimate goal of reading is to extract the meaning or semantic information from a stream of visual symbols. Traditional information-processing models organize reading processes along two main dimensions or routes (Coltheart, Curtis, Atkins, & Haller, 1993; Morton, 1979). Reading through the direct route involves visual recognition of familiar letter combinations as whole words, thus providing access to wholeword semantic and phonological (i.e., sounds of words in speech) representations. The indirect route of reading dominates word identification when letter combinations are not recognized visually as whole words; for example, in the cases of infrequently encountered or new words. In these cases, words are identified through a process of translating the visual subcomponents of words into corresponding phonological elements (i.e., grapheme-to-phoneme conversion) that can be assembled into wholeword phonology and can provide access to semantic information. Informationprocessing models, however, fail to account for a number of experimental findings, such as certain aspects of nonword pronunciation (cf. Seidenberg, Plaut, Petersen, McClelland, & McRae, 1994). In response, recent cognitive models emphasizing neural connectivity and distributed processing (Plaut, McClelland, & Seidenberg, 1995; Seidenberg & McClelland, 1989) or neuropsychological connectivity (Ellis & Young, 1988; Posner & Carr, 1992), which can account for findings not explained by the dual-route models, have generally superseded information-processing models. Despite fundamental differences in the various cognitive models, all emphasize a critical role for phonological processing in word recognition. Unlike spoken language, reading is a skill acquired deliberately through tremendous effort. From a developmental perspective, reading is grafted upon an acquired spoken language. The acquisition of phonological processing skills, such as the ability to segment words into corresponding speech sounds or assemble speech sounds into corresponding letter combinations, is believed critical to the development of efficient reading. Indeed, disorders of phonological processing typically underlie the severe reading disorder of dyslexia (Bradley & Bryant, 1982; Shaywitz et al., 1996). Neuropsychological and functional neuroimaging studies have identified several brain regions involved in basic phonological processes involved in reading. The brain regions most commonly observed as activated in functional imaging studies of normal readers include the left-hemisphere inferior frontal cortex (Brodmann’s area [BA] 44 and 45), left posterior inferior temporal lobe (BA 37), and the left supramarginal gyrus (BA 40) (for reviews, see Poeppel, 1996; Price, 1997). These neurofunctional associations have been determined primarily through paradigms using various rhyming matching tasks. Although valuable, overreliance on one particular method may limit understanding of the complexity of phonological processing. In this report we describe behavioral and neuroimaging findings in which phonological processing was examined by way of repetition priming lexical decision (LD) tasks. In the LD tasks, participants judged whether visually presented letter strings were spelled like genuine English words. Repetition priming refers to the phenomenon that the presentation of a word can alter the subsequent processing of that word, even in the absence of conscious recollection of the initial presentation. The typical LD repetition priming effect is that words are judged more quickly on subsequent presentations. Previous research has shown the LD task to be sensitive and reliable in measuring brain activity and behavior changes due to lexical retrieval (Rugg, 1995; Van Petten, Kutas, Kluender, Mitchner, & McIsaac, 1991). Memory for the phonological properties of words was investigated by using different types of nonword stimuli in each of the LD tasks. One LD task used pseudohomophone nonwords,

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which were nonword letter strings that when decoded sounded like genuine English words (e.g., jale, brane, phocks); the other LD task used pseudoword nonwords, which when decoded did not sound like genuine English words (e.g., muvel, sterve, plont). Functional magnetic resonance imaging (fMRI) was used to identify brain regions sensitive to the repetition priming effect. We predicted that all three stimulus types would engage phonological processing skills, but only words and pseudohomophones would engage neural systems that are sensitive to the recognition of familiar words. Thus, brain regions for phonological analysis and synthesis for word recognition would be observed to be active during word and pseudohomophone processing, but not pseudoword processing. STUDY 1

Method Participants. Fifteen healthy, right-handed, native English speaking volunteers (9 female) were tested. The participants had a mean age of 26.1 (SD ⫽ 8.7) and a mean of 15.1 years of education (SD ⫽ 1.6). None of the participants had a prior diagnosis of dyslexia, attention-deficit disorder, or attentiondeficit hyperactivity disorder. All participants scored in the average range or above (standard score ⱖ 90) on an abbreviated intelligence test (Block Design/Vocabulary subtests of Wechsler Adult Intelligence Scale—Revised or Kaufman Brief Intelligence Test) and two tests of phonological processing: Rosner Auditory Analysis Test (Rosner & Simon, 1971) and Fullerton Auditory Synthesis Test (Thorum, 1980). Design and procedure. Each participant was tested in the pseudohomophone-based (PH) and Pseudoword-based (PW) lexical decision tasks with each task repeated once. In the PH task, participants were instructed to indicate via button responses (right ⫽ ‘‘yes,’’ left ⫽ ‘‘no’’) whether visually presented stimuli were genuine English words based on spelling (stimulus presentation duration 500 ms with 2000 ms between stimulus onsets). Stimuli consisted of 48 common English words (word frequency 50 to 250 per million) (Baayen, Piepenbrock, & van Rijn, 1993) and 48 nonword letter strings that sounded like English words when pronounced (pseudohomophones; e.g., phocks, brane). Participants were instructed to make their judgments as quickly and accurately as possible. The task design used four blocks that alternated between the presentation of an illuminated display for 21 s (rest block) and 48 s of stimulus presentation (task block). An additional rest block was presented following the final task block for analysis purposes. Within the first task block, 18 words and 6 pseudohomophones were presented. In the second task block, 18 new pseudohomophones and 6 new words were presented. The third and fourth task blocks repeated the 18 words and 18 pseudowords, respectively, mixed with 6 new pseudohomophones and 6 new words, respectively. A total of approximately 29 intervening stimuli (⬃114 s) were shown between repetition of identical stimuli. The presentation order of words and pseudohomophones within blocks was randomized. The PW task was identical to the PH task except that the nonword stimuli did not sound like genuine English words when pronounced (pseudowords; e.g., muvel, bastome). The testing order of PH and PW tasks was randomized across participants. Stimulus presentation was conducted and reaction time and accuracy measures recorded via a Macintosh Powerbook 3400c using PsyScope Version 1.2 (Cohen, MacWhinney, Flatt, & Provost, 1993). fMRI acquisition. Imaging was performed with a 1.5 T MRI scanner (General Electric Medical Systems Signa, revision 5.3, Waukesha, WI) using single-shot gradient-recalled echo-planar imaging (TR ⫽ 3000 ms, TE ⫽ 40 ms, flip angle ⫽ 90°, FOV ⫽ 24 cm). High-order phase correction was used to eliminate the common Nyquist ghost artifact in EPI images (Jesmanowicz, Wong, & Hyde, 1993). A field map was used to correct geometric distortions from local field inhomogeneities. Mild diffusion weighting was incorporated to eliminate the contaminations from nearby draining veins (Song, Wong, Tan, & Hyde, 1996). Twenty-one contiguous 5-mm slices were acquired in the brain during each image (voxel size ⫽ 3.75 ⫻ 3.75 mm). One hundred images were collected in each task using a blocked resting condition–test condition design. Seven images were collected in each resting condition (R) followed by 16 images in each test condition (T); the 100 images were collected in the following manner: 7R–16T– 7R–16T–7R–16T–7R–16T–8R. The last image of the last R block had a TE offset and was used to obtain a magnetic field map to correct for geometric distortion (Weisskoff & Davis, 1992). A prescanning routine was used immediately prior to the collection of the images to reduce the effects of T1 contamination on the initially acquired images. fMRI analysis. Motion artifact was examined via a visual examination of the images acquired from each individual participant and was found not to be significant in any of the 15 participants. Functional and anatomical images were registered within each subject (Woods, Grafton, Watson, Sicotte, & Mazzi-

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FIG. 1. Reaction times (RT) to correctly judge stimuli as words or nonwords for 9 participants in PH and PW lexical decision tasks and the orthographic decision task (mean of median RT). Solid bars indicate first judgment reaction time and striped bars indicate second judgment reaction time. Error bars signify SEM.

otta, 1998a) and then registered in 3D to a standard brain image (Woods, Grafton, Watson, Sicotte, & Mazziotta, 1998b) in the Talairach coordinate system (Talairach & Tournoux, 1988). The standard image consisted of 47 slices with a resolution of 121 ⫻ 95 voxels (voxel size in-plane ⫽ 1.5 ⫻ 1.5 ⫻ 3-mm thickness). The fMRI time series were analyzed using a four-way ANOVA (stimulus type, subject, task repetition, and scan replication within block) after normalization to the average signal intensity of the fMRI images (Woods, 1996). Normalization was done to correct for artifactual low-frequency drift in the fMRI images. The ANOVA method required an equal number of rest and task images. The first two images in each of the first four rest and task conditions were ignored because of hemodynamic delay effects. For the analyses, the 3rd through 5th image of each of the four rest conditions and the 3rd through the 14th images of each task condition were analyzed. Thus, the final fMRI data set included one block of 12 resting condition images and four blocks of 12 images from each of the task conditions. Linear contrasts were computed comparing mean voxel intensities. The model assumed that there were no interactions between variables. A Bonferroni correction was used to compute a t value corresponding to an overall p value of .05 (t ⫽ 7.31).

Results and Discussion Repetition priming was measured behaviorally as a change in the reaction time to correctly judge words and nonwords from the first to second stimulus presentation. The reaction time results for the judgment of words, pseudohomophones, and pseudowords in the PH and PW tasks are shown in Fig. 1. Because of technical difficulties in collecting behavioral responses in the MR scanner environment, the reaction time measures from six participants were not available for analysis. Observation of the six participants not included in the analysis indicate nothing unusual in their performance during scanning. We submit that the results from the nine participants available for analysis are representative of the group as a whole. The combined results from the two LD tasks were analyzed using a 4 ⫻ 2 repeated-measures ANOVA with stimulus and repetition as factors. There was a significant stimulus ⫻ repetition interaction, F (3, 24) ⫽ 3.2, p ⬍ .05, and main effects for stimulus, F (3, 24) ⫽ 14.0, p ⬍ .001, and repetition, F (1, 8) ⫽ 28.0, p ⬍ .01. Post-hoc analyses (Bonferroni-corrected t tests) indicated that words in both LD tasks and pseudohomophones were judged more quickly on the second presentation than on the first. Reaction times to make pseudoword judgments were similar on both presentations.

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TABLE 1 Localization of fMRI Priming-Related Effects in Primary Auditory Cortex (Transverse Gyrus of Heschl) Maximum voxel Task

Stimulus

PH PH PW PW OD OD

W PH W PW W PH

x ⫺48 ⫺45 ⫺48 None None None

y

Center of mass z

⫺26 12 ⫺26 12 ⫺24 12 observed observed observed

x ⫺48 ⫺46 ⫺48 None None None

y

z

⫺26 13 ⫺25 12 ⫺24 12 observed observed observed

t value

∆

Cluster size

8.50 7.56 8.15

⫺ ⫺ ⫹

6 3 7

Note. PH task, lexical decision (LD) task using pseudohomophone nonwords; PW task, LD task using pseudoword nonwords; OD, orthographic decision task; W, words; PH, pseudohomophones; PW, pseudowords; x, y, and z coordinates are given in reference to the atlas of Talairach and Tournoux (1988). ∆, direction of fMR signal change: ⫺, repetition suppression of fMR signal (1st stimulus presentation signal ⬎ 2nd stimulus presentation signal; ⫹, repetition enhancement of fMR signal (1st signal ⬍ 2nd signal). Cluster size is the number of contiguous activated voxels (voxel size in-plane ⫽ 1.5 ⫻ 1.5 ⫻ 3-mm thickness).

Functional brain maps of the LD repetition priming effects were constructed by analyzing differences in the fMR activation observed on the first and second presentations on the four types of stimuli using an analysis of variance (Woods, 1996). As shown in Table 1 and Fig. 2, a region within left-hemisphere primary auditory cortex showed a repetition suppression effect for words and pseudohomophones in the PH

FIG. 2. Changes in fMR signal in the primary auditory cortex (transverse gyrus of Heschl, Brodmann’s area 41) between the first and second presentation of word and nonword stimuli in three word judgment tasks. The left brain hemisphere is shown on the left. These brain slices are equivalent to ⫹13.5 mm of the Talairach and Tournoux atlas (Talairach & Tournoux, 1988). White signifies a significant reduction in fMR signal on the second stimulus presentation relative to the first, and black signifies a significant signal increase (p ⬍ .05). In the left panel arrows indicate fMR signal decreases were observed for both words and pseudohomophones in left-hemisphere primary auditory cortex during the PH task. An fMR signal increase was observed in the left hemisphere for words, but not pseudowords, during the PW task (middle panel). The differences in decreased and increased signal across the two tasks suggests that strategic factors influenced activity in this brain region. No primary auditory cortex activation was observed in the OD task for words or pseudohomophones (right panel). This task, unlike the LD task, did not require the whole word identification for successful task performance.

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task (i.e., decreased activity across the two judgments). Pseudowords were not associated with activity changes in this region. This negative finding does not necessarily imply that visual reading of pseudowords did not involve primary auditory cortex processing, only that the fMR activity did not differ significantly between the first and second repetition of pseudowords. As mentioned above, three brain regions have been observed to be activated across a range of tasks that involve phonological processing (Price, 1997): left-hemisphere inferior temporal cortex (BA 37), left inferior frontal cortex (BA 45), and left supramarginal gyrus (BA 40). As shown in Table 2, all of these regions proved sensitive to the priming effect in the two LD tasks. Moreover, the pattern of repetition suppression and repetition enhancement effects across the three stimulus types showed that this type of priming task can provide important information about processing within these regions. For example, findings of repetition enhancement and repetition suppression within a similar Brodmann region and/or anatomical region (e.g., inferior temporal gyrus) suggest that such regions may be subdivided in terms of functional processes. The implications of such activation differences are reported elsewhere (Haist et al., 1999). The overall size of the repetition priming activity is relatively small. In part, this is due to our use of a Bonferroni correction procedure optimized for whole-brain analysis. A region of interest approach focused on the primary auditory cortex might have revealed more extensive activation in this region. The observed active region covers a volume ranging from approximately 33 to 77 mm3 within the primary auditory cortex, or approximately 2.5 to 6.5% of the entire volume of primary auditory cortex. In absolute terms, however, the region where we might reasonably expect to see activation in primary auditory cortex is likely much smaller than the entire priTABLE 2 Activation Observed in the Lexical Decision Tasks in Brain Regions Reported Previously to be Involved in Phonological Processing Max voxel Task

Stimulus

x

PH PH PH PH PW PW PW

W W PH PH W PW PW

⫺54 ⫺51 ⫺57 ⫺48 ⫺51 ⫺63 ⫺51

PH PH PH PH PW PW

W W PH PH W PW

⫺60 ⫺48 ⫺48 ⫺54

PH PH PW PW

W PH W PW

⫺60 ⫺66 ⫺66 ⫺60

y

Center mass z

x

y

z

Left inferior temporal cortex (BA 37) ⫺56 ⫺12 ⫺54 ⫺56 ⫺13 ⫺36 ⫺18 ⫺50 ⫺38 ⫺19 ⫺54 ⫺12 ⫺56 ⫺58 ⫺13 ⫺56 ⫺18 ⫺50 ⫺53 ⫺18 ⫺60 ⫺15 ⫺50 ⫺62 ⫺15 ⫺42 ⫺12 ⫺61 ⫺44 ⫺13 ⫺42 ⫺9 ⫺50 ⫺42 ⫺9 Left inferior frontal cortex (BA 45) 22 21 ⫺59 19 23 44 3 ⫺48 43 3 28 3 ⫺49 32 8 34 6 ⫺54 35 5 none none 20 21 ⫺59 18 22 Left supramarginal gyrus (BA 40) ⫺34 33 ⫺66 ⫺34 33 ⫺50 27 ⫺65 ⫺50 30 none none ⫺30 30 ⫺60 ⫺30 29

t value

∆

Cluster size

13.0 9.5 13.8 13.8 12.2 8.1 8.3

⫺ ⫹ ⫺ ⫹ ⫺ ⫺ ⫹

42 12 67 105 58 9 5

14.1 11.0 10.2 9.9

⫺ ⫹ ⫺ ⫹

35 15 44 5

11.6

⫺

24

8.9 11.2

⫹ ⫹

5 15

11.1

⫺

11

Note. Brain regions observed to be activated in previous studies using tasks sensitive to phonological processing (Price, 1997). See Table 1 for definition of abbreviations.

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mary auditory cortex. Based on previously reported histological analyses of three human brains (Galaburda & Sanides, 1980), the total size of primary auditory cortex is approximately 1200 mm3. Primary auditory cortex is roughly tonotopically organized (cf. Brugge & Merzenich, 1973). Given the phonological nature of this task, we propose that whatever role primary auditory cortex may play in the repetition priming effect, only those aspects of primary auditory cortex which are sensitive to the frequency range of human speech are involved. As expected, second judgments for words on both the PH and the PW tasks were faster on average than the first judgments. This is the prototypical repetition priming effect, suggesting that words are processed more efficiently due to recent experience (Scarborough, Cortese, & Scarborough, 1977; Smith, Colin, Bain, Hoppe, & Richard, 1989). Also expected and paradigmatic was the fact that pseudowords did not show a benefit in judgment reaction time following recent exposure. Pseudohomophone stimuli, however, showed a priming effect similar to that of word stimuli. Pseudowords and pseudohomophones are identical at the level of visual word analysis. The finding that pseudohomophones show reaction time benefits from recent exposure, whereas pseudowords show no such benefit, is consistent with the proposal that pseudohomophones are processed similarly to real words at the level of phonological analysis. Note also that pseudohomophones required more time to judge correctly on the first presentation than did either pseudowords or words. This finding suggests that participants had more difficulty correctly judging pseudohomophones as nonwords because they are genuine words at the phonological level of analysis, thereby generating cognitive competition (Parkin & Ellingham, 1983; Seidenberg, Petersen, MacDonald, & Plaut, 1996). The behavioral priming effect for pseudohomophones appears to be a manifestation of changes in a brain system or systems involved in phonological word recognition. Ascribing aspects of phonological processing to specific brain regions has been controversial in both functional neuroimaging studies and neuropsychological studies of brain-damaged patients (Poeppel, 1996; Price, 1997). However, activation of the primary auditory cortex (transverse gyrus of Heschl) is credible evidence of such phonological processing. Morever, additional activation was observed in brain areas described previously as involved in phonological processes. The repetition priming effect in primary auditory cortex was observed for phonologically familiar words and pseudohomophones only, and not for the phonologically unfamiliar pseudowords. This suggests that the neural system that includes the primary auditory cortex is particularly sensitive to whole-word phonological recognition. In order to examine this issue, a second study was conducted using a task that did not require whole-word identification for successful judgments. The same 15 participants were tested in an orthographic decision task (OD). The OD task was virtually identical to the LD tasks except that the instructions required the participants to judge whether words and pseudohomophones contained at least one instance of the letter ‘‘e.’’ STUDY 2

Method Participants. The same 15 participants that participated in Study 1 were tested. Design and procedure. Each subject was tested in the OD task twice. The tasks were designed and administered identically to that described for the PH task in Study 1, with the exception that participants were instructed to indicate via button responses (right ⫽ ‘‘yes,’’ left ⫽ ‘‘no’’) whether each stimuli contained at least on instance of the letter ‘‘e.’’ Subjects were instructed to make their judgments as quickly and accurately as possible.

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Results and Discussion The reaction time results for the judgment of words and pseudohomophones in the OD task are shown in Fig. 1 (results are from the same nine participants as in Study 1). The reaction time results were analyzed using a 2 ⫻ 2 repeated-measures ANOVA with stimulus and repetition as factors. Only the main effect of stimulus was reliable, F (1, 8) ⫽ 7.4, p ⬍ .05, indicating that words were judged overall more quickly than pseudohomophones and no repetition priming effect was observed for either stimulus type. The functional brain maps of the OD repetition priming effect are shown in Fig. 2. No fMR signal changes were observed in the area of the left primary auditory cortex in conjunction with the repetition effect. Taken in conjunction with the results from Study 1, it appears that the primary auditory cortex fMR priming effect is observed only when phonologically familiar stimuli are recognized at the whole-word level of analysis. GENERAL DISCUSSION

Although speculative, we propose that the fMR priming effects for words differ as a result of the behavioral demands of the two LD tasks. Traditionally, the LD task is viewed as a test of orthographic processes (e.g., whole-word visual recognition) rather than phonological processes. Nevertheless, psychological findings suggest that phonological processes are engaged during visual reading even when reading is automatized and more orthographically controlled (Coltheart, Patterson, & Leahy, 1994). Clearly, the current tasks may demand heightened phonological processing than might be found in typical reading. The two LD tasks presented here differ importantly in the role to which phonological information can be used to make correct word/nonword judgments. Specifically, in the PH task, the similarity of pseudohomophones to genuine words at the phonological level suggests that phonological information would prove inadequate to make correct word/nonword decisions and might be deemphasized accordingly. The repetition suppression effect observed in the fMR images corresponds with a reduction in the usefulness of phonological information. On the other hand, phonological information might be used to advantage in the PW task wherein words and pseudowords differ at both the orthographic and the phonological levels of representation. The repetition enhancement effect for words is consistent with the increased utility of phonological information across repetitions. According to this interpretation, the brain system(s) engaged in these tasks adapted over repetitions of stimuli to either emphasize or deemphasize the use of phonological information. These repetition priming results link primary auditory cortex with a brain system involved in visual word recognition. We observed activation in primary auditory cortex only when comparing fMR activity across repetitions of words and pseudohomophones; that is, activation was observed only in conjunction with the repetition priming effect. We did not observe significant differences in fMR activity in this region when we compared the first presentation of words or pseudowords to a resting condition baseline (i.e., illuminated screen). In recent years, repetition priming studies have proven successful in identifying brain structures involved in language, most notably with respect to orthographic word form analysis (Schacter, Alpert, Savage, Rauch, & Albert, 1996; Squire et al., 1992) and semantic knowledge access (Gabrieli et al., 1996). Our results extend the utility of these paradigms into phonological analysis. Primary auditory cortex involvement in a whole-word visual reading brain system

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has significant implications for theories of normal reading and reading disabilities. Most information-processing models of reading emphasize that reading is a skill grafted onto an acquired spoken language system. Our results suggest that higherorder association areas involved in phonological word form analysis access information provided by primary auditory cortex in a top-down fashion. The exact nature of the information provided by primary auditory cortex in this system is unclear. It does not appear that primary auditory cortex is necessary in skilled readers. Indeed, lesions of the left-hemisphere primary auditory cortex typically result in a syndrome known as pure word deafness, wherein reading, writing, and production of spoken language are generally intact, but the ability to comprehend spoken language is severely impaired (Phillips & Farmer, 1990; Polster & Rose, 1998). Results from psychoacoustic studies of patients with pure word deafness suggest that these patients may have a specific difficulty in temporal processing of speech sounds (Phillips, 1993). Temporal processing deficits in early sensory processing systems, and in particular auditory processing systems, may underlie some language disabilities including dyslexia (Tallal, Galaburda, Llina´s, & von Euler, 1993). One interpretation of the role of primary auditory cortex is that it contributes temporal information in phonological analysis and synthesis in visual word recognition. At this time, however, we are unable to determine which of several candidate brain regions interconnected with primary auditory cortex is accessing the information provided by this region. More definitive statements of the functional significance of primary cortex activity must remain until more information is available about the brain regions that are accessing the information provided by primary auditory cortex. REFERENCES Baayen, R. H., Piepenbrock, R., & van Rijn, H. (1993). The CELEX lexical database [CD-ROM]. Philadelphia: Linguistic Data Consortium, Univ. of Pennsylvania. Bradley, L., and Bryant, P. E. (1982). Categorising sounds and learning to read: A causal connection. Nature, 310, 419–421. Brugge, J. F., & Merzenich, M. M. (1973). Responses of neurons in the auditory cortex of the macaque monkey to monaural and binaural stimulation. Journal of Neurophysiology, 36, 1138–1158. Cohen, J. D., MacWhinney, B., Flatt, M., & Provost, J. (1993). PsyScope: A new graphical interactive environment for designing psychology experiments. Behavioral Research Methods, Instruments, and Computers, 25(2), 257–271. Coltheart, M., Curtis, B., Atkins, P., & Haller, M. (1993). Models of reading aloud: Dual-route and parallel distributed processing approaches. Psychological Review, 100, 589–608. Coltheart, V., Patterson, K., & Leahy, J. (1994). When a ROWS is a ROSE: Phonological effects in written word comprehension. The Quarterly Journal of Experimental Psychology, 47A(4), 917– 955. Diamond, J. (1997). Guns, germs, and steel: The fates of human societies. New York: Norton. Ellis, A. W., & Young, A. W. (1988). Human cognitive neuropsychology. Hove and London: Erlbaum. Gabrieli, J. D. E., Desmond, J. E., Demb, J. B., Wagner, A. D., Stone, M. V., Vaidya, C. J., & Glover, G. H. (1996). Functional magnetic resonance imaging of semantic memory processes in the frontal lobes. Psychological Science, 7(5), 278–283. Galaburda, A., & Sanides, F. (1980). Cytoarchitectonic organization of the human auditory cortex. Journal of Comparative Neurology, 190, 597–610. Jesmanowicz, A., Wong, E. C., & Hyde, J. S. (1993). Phase correction for EPI using internal reference lines. In Proceedings of the Society of Magnetic Resonance Medicine, 1239. Morton, J. (1979). The interaction of information in word recognition. Psychological Review, 76, 165– 178. Parkin, A. J., & Ellingham, R. (1983). Phonological recoding in lexical decision: The influence of pseudohomophones. Language and Speech, 26(1), 81–90. Phillips, D. P. (1993). Neural representation of stimulus times in the primary auditory cortex. In P. Tallal,

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