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The representation of letter position: Evidence from dysgraphia
Brain and Language 103 (2007) 8–249 www.elsevier.com/locate/b&l
The representation of letter position: Evidence from dysgraphia Simon Fischer-Baum *, Brenda Rapp, Michael McCloskey Department of Cognitive Science, Johns Hopkins University, 3400 N. Charles Street, Baltimore, MD 21218, USA
The orthographic representations that underlie our ability to spell words must encode not only the letters in each word, but also the positions of the letters. How, though, is position represented? For example, is the G in DOG the third letter, the first letter to the right of center, or the last letter? Several position-encoding schemes have been proposed, but relevant evidence is sparse. We present evidence from two dysgraphic individuals bearing directly on the issue. We consider three position-representation hypotheses: left-aligned, center-aligned, and edge-aligned, illustrated in the table below. Note, for example, that the N in BARN is in the same position as the O in DEPORT by the left-aligned account, the R by the center-aligned account, and the T by the edge-aligned account.
Left-aligned 1 D B F
2 E A I
3 P R L
Center-aligned 4 O N M
5 R
6 3 T D
2 E B F
1 P A I
+ 1 O R L
Edge-aligned + 2 R N M
+ L 3 1 T D B F
L 2 E A I
L 3 P
R R 3 2 O R R L
R 1 T N M
of the five previous responses more often than would be expected by chance (p < .0001). Additional analyses showed that for each subject the perseveration errors arose at a level of abstract orthographic representations.
Experimental study We used the subjects’ letter perseveration errors to examine the representation of letter position. For each subject, we analyzed errors in which (a) a single letter was intruded (e.g., CHANGE for CHANCE) and (b) the intruded letter (e.g., G) was a potential perseveration, because it was present in one or more of the five immediately preceding responses (e.g., ROUGH). We refer to the response with the intruded letter (e.g., CHANGE) as the perseveration response, and the most recent preceding response that included this letter (e.g., ROUGH) as the source response. We addressed two questions. First, did the subjects’ perseveration errors maintain position – that is, did the intruded letter appear in the same position in the source and perseveration responses more often than expected by chance? Second, according to what position-encoding scheme(s) was position maintained? Is position maintained?
Cases LSS, a left-handed man with a master’s degree, suffered a stroke at age 54. CM, a right-handed man with a Ph.D., suffered a stroke at 59. For both, CT showed extensive damage in the distribution of the left middle cerebral artery. Perseveration errors In writing words to dictation both subjects frequently produced letters that did not appear in the correct spelling (e.g., the G in CM’s spelling of CHANCE as CHANGE). These intruded letters were frequently letters that had appeared in immediately preceding responses (e.g., ROUGH), suggesting that the intrusions often were perseverations from the earlier responses. Analyses described in McCloskey, Macaruso, and Rapp (2006) revealed that letters intruded into a response were present in each
*
Corresponding author. E-mail address: fi[email protected] (S. Fischer-Baum).
doi:10.1016/j.bandl.2007.07.064
We addressed this question by means of an analysis that did not depend upon any particular position-encoding scheme. Specifically, we analyzed source-perseveration pairs in which the two responses were of the same length. Consider the following pair:
Source response Perseveration response
Target
Response
BARN FILM
BARN FIRM
Because BARN and FIRM have the same number of letters, the B, A, R, and N in BARN are in the same positions as the F, I, R, and M in FIRM, respectively, regardless of how we define position. Hence, we can straightforwardly determine that the intruded letter (i.e., R) occupied the same position in the source (BARN) and perseveration (FIRM) responses. We tabulated the proportion of source-perseveration pairs in which position was maintained, and also calculated the proportion expected by chance. Briefly, the chance analysis assessed how often the position of
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Abstract / Brain and Language 103 (2007) 8–249
the intruded letter in the perseveration response matched the position of that letter in same-length control responses that were distant from the perseveration response in the trial sequence (and so could not plausibly have been actual sources of the perseverated letter). Monte Carlo simulations established that for both CM and LSS, the perseverations maintained position far more often than expected by chance (p < .0001).
position at above chance rates. In the edge-aligned vs. center-aligned comparison, neither subject maintained center-aligned position at above chance rates. In contrast, CM maintained edge-aligned position more often than expected by chance (p < .01), and LSS’s tendency to maintain edge-aligned position approached significance (p = .11). Conclusions
What type of position is maintained? We dissociated the alternative position-representation hypotheses by analyzing source-perseveration pairs in which the two responses differed in length. Consider the following pair:
Source response Perseveration response
Target
Response
DEPORT FILM
DEPORT FIRM
The subjects’ perseveration errors maintained letter position more often than would be expected by chance. Of the three hypotheses tested, the edge-aligned hypothesis best fits the data. Interestingly, competitive queueing simulations of spelling (Houghton, Glasspool, & Shallice, 1994) have similarly represented position based on distance from both the beginning and end of the word, and similar encoding schemes have also been proposed for other cognitive processes (e.g., short-term memory for serial order; Henson, 1998). References
The R in FIRM has the same position as the P in DEPORT by the leftaligned hypothesis, the O by the center aligned-hypothesis, and the R by the edge-aligned hypothesis. Hence, the R maintains position only as defined by the edge-aligned hypothesis. We carried out two analyses, one that distinguished the edge-aligned from the left-aligned hypothesis, and another that distinguished the edge- and center-aligned hypotheses. In the edge- vs. left-aligned comparison, both LSS’s and CM’s errors maintained edge-aligned position more often than expected by chance (p < .02 and .001, respectively). Neither subject maintained left-aligned
Henson, R. N. A (1998). Short-term memory for serial order: the start-end model. Cognitive Psychology, 36, 73–137. Houghton, G., Glasspool, D. W., & Shallice, T. (1994). Spelling and serial recall: Insights from a competitive queueing model. In G. D. A. Brown & N. C. Ellis (Eds.), Handbook of spelling: Theory, process and intervention. Wiley: Chichester. McCloskey, M., Macaruso, P., & Rapp, B. (2006). Grapheme-to-Lexeme feedback in the spelling system: Evidence from a dysgraphic patient. Cognitive Neuropsychology, 23, 278–307.
The representation of letter position: Evidence from dysgraphia Simon Fischer-Baum *, Brenda Rapp, Michael McCloskey Department of Cognitive Science, Johns Hopkins University, 3400 N. Charles Street, Baltimore, MD 21218, USA
The orthographic representations that underlie our ability to spell words must encode not only the letters in each word, but also the positions of the letters. How, though, is position represented? For example, is the G in DOG the third letter, the first letter to the right of center, or the last letter? Several position-encoding schemes have been proposed, but relevant evidence is sparse. We present evidence from two dysgraphic individuals bearing directly on the issue. We consider three position-representation hypotheses: left-aligned, center-aligned, and edge-aligned, illustrated in the table below. Note, for example, that the N in BARN is in the same position as the O in DEPORT by the left-aligned account, the R by the center-aligned account, and the T by the edge-aligned account.
Left-aligned 1 D B F
2 E A I
3 P R L
Center-aligned 4 O N M
5 R
6 3 T D
2 E B F
1 P A I
+ 1 O R L
Edge-aligned + 2 R N M
+ L 3 1 T D B F
L 2 E A I
L 3 P
R R 3 2 O R R L
R 1 T N M
of the five previous responses more often than would be expected by chance (p < .0001). Additional analyses showed that for each subject the perseveration errors arose at a level of abstract orthographic representations.
Experimental study We used the subjects’ letter perseveration errors to examine the representation of letter position. For each subject, we analyzed errors in which (a) a single letter was intruded (e.g., CHANGE for CHANCE) and (b) the intruded letter (e.g., G) was a potential perseveration, because it was present in one or more of the five immediately preceding responses (e.g., ROUGH). We refer to the response with the intruded letter (e.g., CHANGE) as the perseveration response, and the most recent preceding response that included this letter (e.g., ROUGH) as the source response. We addressed two questions. First, did the subjects’ perseveration errors maintain position – that is, did the intruded letter appear in the same position in the source and perseveration responses more often than expected by chance? Second, according to what position-encoding scheme(s) was position maintained? Is position maintained?
Cases LSS, a left-handed man with a master’s degree, suffered a stroke at age 54. CM, a right-handed man with a Ph.D., suffered a stroke at 59. For both, CT showed extensive damage in the distribution of the left middle cerebral artery. Perseveration errors In writing words to dictation both subjects frequently produced letters that did not appear in the correct spelling (e.g., the G in CM’s spelling of CHANCE as CHANGE). These intruded letters were frequently letters that had appeared in immediately preceding responses (e.g., ROUGH), suggesting that the intrusions often were perseverations from the earlier responses. Analyses described in McCloskey, Macaruso, and Rapp (2006) revealed that letters intruded into a response were present in each
*
Corresponding author. E-mail address: fi[email protected] (S. Fischer-Baum).
doi:10.1016/j.bandl.2007.07.064
We addressed this question by means of an analysis that did not depend upon any particular position-encoding scheme. Specifically, we analyzed source-perseveration pairs in which the two responses were of the same length. Consider the following pair:
Source response Perseveration response
Target
Response
BARN FILM
BARN FIRM
Because BARN and FIRM have the same number of letters, the B, A, R, and N in BARN are in the same positions as the F, I, R, and M in FIRM, respectively, regardless of how we define position. Hence, we can straightforwardly determine that the intruded letter (i.e., R) occupied the same position in the source (BARN) and perseveration (FIRM) responses. We tabulated the proportion of source-perseveration pairs in which position was maintained, and also calculated the proportion expected by chance. Briefly, the chance analysis assessed how often the position of
102
Abstract / Brain and Language 103 (2007) 8–249
the intruded letter in the perseveration response matched the position of that letter in same-length control responses that were distant from the perseveration response in the trial sequence (and so could not plausibly have been actual sources of the perseverated letter). Monte Carlo simulations established that for both CM and LSS, the perseverations maintained position far more often than expected by chance (p < .0001).
position at above chance rates. In the edge-aligned vs. center-aligned comparison, neither subject maintained center-aligned position at above chance rates. In contrast, CM maintained edge-aligned position more often than expected by chance (p < .01), and LSS’s tendency to maintain edge-aligned position approached significance (p = .11). Conclusions
What type of position is maintained? We dissociated the alternative position-representation hypotheses by analyzing source-perseveration pairs in which the two responses differed in length. Consider the following pair:
Source response Perseveration response
Target
Response
DEPORT FILM
DEPORT FIRM
The subjects’ perseveration errors maintained letter position more often than would be expected by chance. Of the three hypotheses tested, the edge-aligned hypothesis best fits the data. Interestingly, competitive queueing simulations of spelling (Houghton, Glasspool, & Shallice, 1994) have similarly represented position based on distance from both the beginning and end of the word, and similar encoding schemes have also been proposed for other cognitive processes (e.g., short-term memory for serial order; Henson, 1998). References
The R in FIRM has the same position as the P in DEPORT by the leftaligned hypothesis, the O by the center aligned-hypothesis, and the R by the edge-aligned hypothesis. Hence, the R maintains position only as defined by the edge-aligned hypothesis. We carried out two analyses, one that distinguished the edge-aligned from the left-aligned hypothesis, and another that distinguished the edge- and center-aligned hypotheses. In the edge- vs. left-aligned comparison, both LSS’s and CM’s errors maintained edge-aligned position more often than expected by chance (p < .02 and .001, respectively). Neither subject maintained left-aligned
Henson, R. N. A (1998). Short-term memory for serial order: the start-end model. Cognitive Psychology, 36, 73–137. Houghton, G., Glasspool, D. W., & Shallice, T. (1994). Spelling and serial recall: Insights from a competitive queueing model. In G. D. A. Brown & N. C. Ellis (Eds.), Handbook of spelling: Theory, process and intervention. Wiley: Chichester. McCloskey, M., Macaruso, P., & Rapp, B. (2006). Grapheme-to-Lexeme feedback in the spelling system: Evidence from a dysgraphic patient. Cognitive Neuropsychology, 23, 278–307.