Ординатура / Офтальмология / Английские материалы / Eye Movements A Window on Mind and Brain_Van Gompel_2007

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Abstract

Previous experiments have shown that transposed-letter (TL) nonwords (e.g., jugde for judge) produce significant priming relative to orthographic controls (e.g., jupte). In fact, masked priming experiments indicate that TL effects exist even when the letter manipulations are nonadjacent, as long as the transposed letters are both consonants (Perea & Lupker, 2004a). This chapter presents data from a new study in which nonadjacent TL effects and the differential effects of vowels and consonants are explored during sentence reading using an eye-contingent display change paradigm. Results indicate that TL effects exist when nonadjacent letter positions are manipulated, suggesting that the coding of letter identities within a word is not specific to the absolute letter position, but is, instead, much more flexible. However, unlike the results of Perea and Lupker, those from the present study indicate that vowels and consonants pattern similarly.

Many current models of visual word recognition assume that letter positions are encoded very early in visual word recognition, even before the encoding of letter identities. Such models include the Multiple Read-Out Model (Grainger & Jacobs, 1996), the Dual Route Cascaded model (Coltheart, Rastle, Perry, Ziegler, & Langdon, 2001), the Interactive Activation Model (McClelland & Rumelhart, 1981), and the Activation Verification Model (Paap, Newsome, McDonald, & Schvaneveldt, 1982). These models all assume a “channel-specific” coding scheme for the processing of letter identities. That is, letter positions are encoded first, followed by the encoding of letter identities within each specific letter position.

One sharp criticism that has been made against these models is that they fail to account for the fact that transposed-letter (TL) nonwords (e.g., jugde) have been found to be more similar to their base words (e.g., judge) than nonwords in which two letters are substituted with other letters (e.g., jupte). This transposed-letter effect is well documented across a number of tasks including naming (Andrews, 1996; Christianson, Johnson, & Rayner, 2005), lexical decision (Andrews, 1996; Chambers, 1979; Forster, Davis, Schoknecht, & Carter, 1987; Holmes & Ng, 1993; O’Connor & Forster, 1981; Perea & Lupker, 2003a, 2003b, 2004a, 2004b; Perea, Rosa, & Gómez, 2005; Schoonbaert & Grainger, 2004), semantic categorization (Taft & van Graan, 1998), and normal silent reading (Johnson, Perea, & Rayner, 2007). Models employing a channel-specific coding scheme incorrectly predict that these two nonwords are equally similar to one another, because in both cases, three of the five letters are in their correct letter position. Findings from such experiments have helped to argue against models of word recognition that suggest a “channel-specific” encoding of letters. It appears that the encoding of letter identities within a word is not dependent upon absolute letter position, but is much more flexible.

While the majority of these studies have found TL effects at the foveal level (i.e., where all stimuli fell within 2 of visual angle around the point of fixation), these effects have recently been found to exist in normal silent reading (Johnson et al., 2007) in which transpositions occurred in the parafovea (i.e., the area extending 4 to the left and 4 to the right beyond the foveal area). Johnson et al. used an eye-contingent display change technique (the boundary paradigm, Rayner, 1975) to manipulate the parafoveal preview readers received prior to fixating on a given target word (Figure 1). The stimuli from Perea and Lupker (2003a) were embedded into sentences and the prime conditions served as parafoveal previews of the target word. Parafoveal previews fell into one of five conditions: (1) identical to the target word (clerk as the preview of clerk), (2) a transposition of two internal letters (celrk), (3) a substitution of two internal letters (cohrk), (4) a transposition of the two final letters (clekr), or (5) a substitution of the two final letters (clefn). Johnson et al. found that the TL effects obtained in masked priming also exist during normal silent reading, where the potential priming information is located to the right of fixation in the parafovea. That is, parafoveal previews involving a transposition of two adjacent letters led to shorter fixation durations than previews involving a substitution of two adjacent letters. For short (five-letter) words, this pattern was true for both internal and final-letter manipulations, but for longer (seven-letter) words, there was no difference

Greg put the wild flewor in a vase at his grandmother’s house.

Greg put the wild flewor in a vase at his grandmother’s house.

Greg put the wild flewor in a vase at his grandmother’s house.

Greg put the wild flower in a vase at his grandmother’s house.

Greg put the wild flower in a vase at his grandmother’s house.

Greg put the wild flower in a vase at his grandmother’s house.

Greg put the wild flower in a vase at his grandmother’s house.

Note: The asterisk located below each sentence indicates the reader’s fixation location. At the onset of the sentence, the target word (here shown in bold) is replaced with one of the three parafoveal previews (in this example, the transposed-letter preview, flewor). When the reader’s eyes cross the invisible boundary (located just to the left of the space immediately preceding the target word), the parafoveal preview of the target word changes to the target word (here, flower) and remains as such until the participant indicates that they have finished reading the sentence.

Figure 1. Example sentence employing the boundary paradigm.

between the transposed and substituted letter (SL) conditions at the word-final position, likely due to acuity constraints.

Thus, it appears that letter identity information can be extracted from the fovea (and the parafovea from the first five letters of the word to the right of fixation) independent of absolute letter position. These experiments also suggest that the encoding of specific letter positions follows some time after the encoding of letter identities. What is unclear, however, is the extent to which letter position does not matter. In the experiments presented so far, all of the TL conditions involved a single transposition of two adjacent letters.1

In a series of experiments using masked-priming techniques, Perea and Lupker (2004a) explored the nature of TL effects with nonadjacent letter manipulations in Spanish. In addition, manipulations involved either vowels (e.g., anamil as the prime for animal) or consonants (e.g., caniso as the prime for casino). The results indicated that when the letter manipulations involved consonants, TL primes led to faster lexical

1 Interestingly, research indicates that transposing the first two letters in a word causes disruption during normal silent reading (Johnson, Perea, & Rayner, 2007) and in masked-priming (Chambers, 1979). Chambers found that word-initial TL nonwords (e.g., omtor for motor) were less similar to their base words than word-internal TL nonwords (liimt for limit).

decision times than SL primes. However, when the letter manipulations involved vowels, there was no significant TL effect. Thus, TL-nonwords involving nonadjacent transpositions can activate the lexical representation of their base words, but only under certain circumstances.

The differential patterning of TL effects among consonants and vowels was further explored by Perea and Lupker (2004b) using English stimuli. Form priming effects were obtained for adjacent consonant transpositions (e.g., hosre–horse vs honce–horse) and for adjacent consonant–vowel transpositions (brcik–brick vs brsok–brick), but there were no priming effects for adjacent vowel transpositions (draem–dream vs droim– dream). These results, then, also support the differences in TL effects across vowels and consonants.

However, in English, the spelling-to-sound correspondences for consonants are much more regular than those for vowels. It would follow that consonants should be coded and processed more rapidly than vowels. This has led many researchers to hypothesize that these two types of letters are processed differently in reading (Berent & Perfetti, 1995). In fact, there has been much data from response time tasks (Perea & Lupker, 2004a, 2004b), silent reading tasks (Lee, Rayner, & Pollatsek, 2001, 2002), and brain-damaged patients (Caramazza, Chialant, Capasso, & Miceli, 2000) that suggest that vowels and consonants do play different roles in visual word recognition. For example, Berent and Perfetti (1995) and Lee et al. (2001, 2002) have data suggesting that at the foveal level, consonants play a greater role than vowels in the early stage of visual word recognition. The contribution of vowel information is just as strong as that of consonants, but plays a role much later in lexical identification.

In light of this previous research, the goal of the current experiment was twofold. First, I sought to investigate whether TL effects exist during normal silent reading when letter manipulations involve nonadjacent letter positions. Although letter identity can be encoded independent of absolute letter position while reading sentences, it could be the case that letter identities can only be encoded outside of their correct letter position when they are displaced one letter position to the left or right (to positions N −1 and N +1). If, however, readers are able to extract useful identity information from the parafovea that falls outside of this region (i.e., in this case, two character positions from the correct location, to positions N −2 and N +2), we would expect to find shorter fixation durations on target words (e.g., flower) preceded by a TL parafoveal preview (e.g., flewor) rather than a SL parafoveal preview (e.g., flawur). Such findings would provide even more support against models suggesting channel-specific encoding strategies.

Secondly, I sought to explore the differential patterning of TL effects that has been found in masked priming lexical decision tasks among vowels and consonants using a parafoveal preview experiment. All previous research on the differential roles of vowels and consonants in visual word recognition has addressed the patterning of these two letter groups when the stimuli (and experimental manipulations) were presented in foveal vision. If vowels and consonants are also processed differently in the parafovea, we might expect to see different patterns of TL-effects for these two types of letters. In the present experiment, TL nonwords (e.g., flewor and fosert) and SL nonwords (e.g., flawur and

fonewt) were presented as parafoveal previews of their base words (e.g., flower and forest, respectively) to explore the role of vowels and consonants in parafoveal processing.

1. Method

1.1. Participants

Thirty-three members of the University of Massachusetts Amherst community who were native speakers of American English participated in the experiment. All participants had normal vision or wore soft contact lenses and were naïve to the purpose of the experiment. At the completion of the experiment, they received course credit or monetary compensation for their time.

1.2. Apparatus

Single-line sentences appeared one at a time on a 15-inch NEC MultiSync 4FGe monitor. Participants were seated 61 cm from the monitor, and at this distance, 3.8 letters equaled 1 of visual angle. The display was refreshed every 5 ms. Eye movements were recorded using a Generation V Fourward Technologies Dual Purkinje Eyetracker interfaced with a Pentium computer. Although reading took place binocularly, eye movements were sampled every millisecond from only the reader’s right eye.

1.3. Stimuli

Thirty-six six-letter target words were embedded into single-line sentences no longer than 76 characters. Target words never occupied the sentence-initial or sentence-final word position and represented a variety of word classes and word frequencies. Three parafoveal preview conditions were created for each target word. In the identity condition, the parafoveal preview was identical to the target word (e.g., flower as the preview of flower). In the TL condition, the preview involved the transposition of the third and fifth letters (e.g., flewor). Finally, in the SL condition, the preview involved the substitution of the third and fifth letters (e.g., flawur). The replacement letters in the SL condition were visually similar to the two transposed letters. That is, vowels were substituted with vowels, consonants were substituted with consonants, ascending letters were substituted with ascending letters, and descending letters were substituted with descending letters. The TL condition and SL condition always maintained the overall word shape as presented in Courier font. For example, fosert was used as a TL nonword for forest (both the letters s and r are neither ascending nor descending) but furute was not used as a TL nonword for future (the letter r is neither ascending nor descending but the letter t is ascending).

In addition to the three parafoveal preview conditions, two types of target words were used. Target words either included (1) vowels at letter positions 3 and 5 (e.g., flower),

or (2) consonants at letter positions 3 and 5 (e.g., forest). The two target word groups were matched for word frequency using both the Francis and Kuceraˇ (1982) frequency count and the Celex Lexical Database (Baayen, Piepenbrock, & Gulikers, 1995). Francis and Kuceraˇ frequencies for the 18 vowel words ranged from 1 to 340 per million (mean = 76). For the 18 consonant words, frequencies ranged from 1 to 301 per million (mean = 76). The frequencies of these two groups did not differ significantly from each other using either of the two frequency counts (t’s < 1).2

Previous research has found that when words are highly predictable from their previous context, they are often skipped (Rayner, 1998). Thus, in order to maximize the likelihood that target words would be fixated, the context leading up to each target word was neutral. In a predictability norming procedure, ten participants were presented with the beginning part of each sentence (up to the target word) and asked to predict the next word in the sentence. All target words were found to be unpredictable from their previous context (mean predictability score = 4.7%). There was also no significant difference in the predictability scores across the two word types (t < 1).

In order to ensure that all of the target words fit well within their sentence context, the sentences were also normed for understandability. Ten participants were asked to rate from one (not understandable) to seven (very understandable) how well each target word fit within its sentence frame. All target words were judged to be highly understandable (mean = 6.5). In addition, there were no significant differences in understandability across the two word types (t < 1). The experimental sentences (including the three parafoveal preview conditions) for each of the two word types are presented in the Appendix.

1.4. Design and procedure

In order to reduce head movements during the experiment, a bite bar and a forehead rest were used. The initial calibration then took place (which lasted roughly 5 min), followed by a practice session involving eight sentences. The experimental session then followed. Each experimental sentence appeared one at a time (in random order) along the center row of the monitor. Readers were told to read each sentence silently at a comfortable pace and to press a response key when finished. In order to investigate the amount of parafoveal information the readers are gaining about a target word before fixating it, the boundary paradigm (Rayner, 1975) was used (see Figure 1). Prior to the presentation of the sentence, a fixation box appeared at the leftmost part of the screen. The experimenter then initiated the onset of the trial in which the sentence appeared on the screen with the first letter of the sentence at the location of the fixation box.

2 Another possible difference between the two word type conditions or the three parafoveal preview conditions includes the mean bigram textual frequency and the mean trigram textual frequency. Although the mean bigram and mean trigram type frequencies of the identity previews (56.93 and 10.24, respectively) were significantly greater than those of the TL (40.38 and 3.84) and SL previews (32.72 and 3.03), there were no significant differences in the mean bigram or trigram type frequencies across the two word type conditions (p’s > 0 24 .

432 R. L. Johnson

The target word appeared in one of the three preview conditions. When the readers moved their eyes to fixate on the target word (crossing the invisible boundary located just to the left of the space immediately preceding the target word), the display changed so that the preview changed to the target word. The display change occurred during the saccade, and the target word then remained throughout the remainder of the trial. Between each trial, the accuracy of the initial calibration was checked before the experimenter initiated the next trial.

Parafoveal preview was a within-subject and within-item variable; word type was a within-subject and between-item variable. Each participant read all 36 experimental sentences (18 of which included a consonant target word and 18 of which included a vowel target word). Items were counterbalanced so that there were 12 sentences in each of the three preview conditions. Thus, there were three counterbalancing conditions. Experimental sentences were presented in random order along with 78 filler sentences. Comprehension questions followed 16% of the trials to ensure that participants were carefully reading the sentences. All of the readers scored above 89% accuracy on the questions (mean = 97%). The entire experimental procedure took less than 30 min.

2. Results

The amount of time spent fixating a word is thought to reflect the time it takes to process that word (Rayner, 1998; Rayner & Pollatsek, 1989). Given that readers can extract useful information from the parafovea prior to fixating a word, parafoveal previews that provide more useful information will lessen the subsequent time the reader spends directly fixating the target word. If the different parafoveal preview conditions provide more or less useful information, we would expect to see differences in fixation times on the target words themselves. Three common measures of the amount of time spent on the target word are first fixation duration, single fixation duration, and gaze duration. First fixation duration is the amount of time spent on the initial fixation of the target word, regardless of whether there is more than one fixation on it. In contrast, single fixation duration is the amount of time spent on the initial fixation of the target word given that there was only one fixation on the first pass reading of the word. Gaze duration is the sum of all fixation durations on the target word before the reader leaves the word.

Trials were eliminated from data analysis if (1) the display change was triggered too early, (2) tracker loss occurred during a trial, or (3) the participant blinked while fixating the pre-target word, target word, or post-target word. In cases in which adjacent fixations fell within one character of one another, and one of the fixations was short (less than 80 ms), the two fixations were pooled (see Rayner, 1998). In addition, extremely short (less than 80 ms) isolated fixations and extremely long (greater than 800 ms) fixations were eliminated from the data. Altogether, 15.8% of the data were eliminated. The mean first fixation durations, single fixation durations, and gaze durations for each of the three parafoveal preview conditions in each of the two word type conditions are shown in Table 1.

Note: All durations for first fixation duration, single fixation duration, and gaze duration are in ms. Word type involved the manipulation of either vowels (V) or consonants (C).

For each of the three dependent fixation duration measures, a 2 (word type: vowels or consonants) by 3 (parafoveal preview: identity control, transposed letters, or substituted letters) Analysis of Variance (ANOVA) was conducted on the data. Error variance was calculated over participants (F 1) and over items (F 2). In addition, planned comparisons were run to compare fixation duration in the TL condition to the respective identity condition and SL condition across the two word types.

The main effect of parafoveal preview was highly significant both by participants and by items across all three viewing duration measures (first fixation: F 1 2 64 = 6 62 p < 0 01; F 2 2 68 = 7 46 p < 0 01; single fixation: F 1 2 64 = 13 87 p < 0 001; F 2 2 68 = 12 90 p < 0 001; gaze duration: F 1 2 64 = 10 33 p < 0 001; F 2 2 68 = 7 50 p < 0 01). For first fixation duration and single fixation duration, this main effect was due to significantly longer viewing durations on target words preceded by SL previews when compared to both identity previews (first fixation: t1 32 = 3 20 p < 0 01; t2 35 = 3 43 p < 0 01; single fixation: t1 32 = 4 75 p < 0 001; t2 35 = 4 58 p < 0 001) and TL previews (first fixation: t1 32 = 3 32 p < 0 01; t2 35 = 2 87 p < 0 01; single fixation: t1 32 = 4 45 p < 0 001 t2 35 = 3 14 p < 0 01). For first fixation duration, there was no significant difference between the identity condition and the TL condition (both t’s < 1), and for single fixation duration, the difference between these two conditions was significant only by items (t1 32 = 1 64 p = 0 11; t2 35 = 2 15 p < 0 05).

In contrast, for gaze duration, this main effect was the result of significantly shorter viewing durations for identity previews when compared to both TL previews (t1 32 = 3 29 p < 0 01; t2 35 = 2 73 p < 0 01) and SL previews (t1 32 = 4 00 p < 0 001; t2 35 = 3 77 p < 0 001). The difference between the TL condition and the SL condition was not significant either by participants or by items (both p’s > 0 12).

The main effect of word type was not significant across any of the viewing duration measures (all F ’s < 1, all p’s > 0 5). Critically, the interaction between parafoveal preview and word type was also not significant across any of the dependent measures (all F ’s < 1, all p’s > 0 55). That is, the same pattern of parafoveal preview facilitation was seen in words in which vowels were transposed as in words in which consonants were transposed.