Sobre la oferta hídrica

Seron and Deloche conducted a series of studies analyzing the ability of aphasie patients to transcode w ritten num ber nam es to arabic nu m erals (i.e. From Three to 3; Deloche an d Seron 1982a, b) an d arabic num erals to w ritten n u m b er nam es (i.e. From 4 to Four; Seron an d D eloche, 1983; 1984). These a u th o rs analyzed the p a tien ts' perform ance in th ese tasks giv in g th e first system atic account of the types of errors produced by the aphasie patients w hen confronted w ith these p articu lar tasks. In ad d itio n , th ey tried to analyze the possible relations existing betw een particular types of transcoding errors and particular types of linguistic disorders in an attem pt to u n d erstan d the n atu re of the underlying cognitive processing mechanisms.

The authors first investigated a m ixed group of 32 aphasie patients on a w ritten num ber nam es to arabic num erals transcoding task (Deloche and Seron, 1982a). Each aphasie patient was given a list of 100 w ritten num ber names. The stim uli w ere of different length and of different "intuitive factors of difficulty". For exam ple, w ritten num ber nam es in which the internal zero, is not indicated, like "cent deux mille six" (102,006), were considered m ore difficult than w ritten num ber names in which the internal zero is indicated. The errors w ere analyzed in term s of:

1. Some general dim ension of the stimuli, such as for exam ple the length of the w ritten num ber names or the length of the expected arabic num eral.

2. Som e general serial o rd e rin g d istu rb an ces, such as n u m b er a d d itio n s, om issions, displacem ents an d perseverations.

3. Som e specific failu res in the ap p licatio n of th e ru les in v o lv ed in the transcoding process.

This last type of analysis turned out to be the m ost adequate since it accounted for a large p ro p o rtio n and type of errors observed. This analysis is based on the authors' psycholinguistic notion that num bers are organized in term s of "stack structure". Stacks are o rd ered one dim ensional arrays: an item belongs to a p a rticu la r stack and has a specified position w ith in the stack. The au th o rs suggested that the elem ents of the French and Belgian (Wallon) num eral lexicon system s are arranged in the following stack structures

1. UNITS num bers from 1 to 9 2. TENS num bers from 10 to 90 3. PARTICULAR num bers from 11 to 16

4. MISCELLANEOUS num bers 1,000; 100; 0 and the w ord et (and)

So, for example, the num ber 2 belonged to the UNIT stack and w ithin the UNIT stack occupied the second position. For the authors the im portance of the notion of stack stru ctu re resides in the claim th at the tw o sets of categorisation in fo rm atio n (the stack an d the position within stack) have u n d e rly in g separable c o g n itiv e p ro cesses. In d eed , the p a tte rn of erro rs fo u n d in th eir aphasie population confirm ed this claim. Patients m ade tw o types of error: stack errors, w here the w rong stack is selected (e.g. 'quinze' (15) - 50), an d errors of position in stack structures, w here a lexical m istake involves the choice of the w rong nam e from the right stack (e.g. 'cinquante-huit' (58) - 59). This n o t only dem onstrate th at stack and position within stack inform ation is functionally in d ep en d en t b u t also that this information can be selectively dam aged by cerebral lesions.

In tw o follow ing w orks the au th o rs co rrelated th e lan g u ag e errors presented by the 7 Broca and 7 W ernicke aphasies patients w ith the errors these p a tien ts com m itted on tw o tran sco d in g tasks: tran sco d in g w ritte n num ber nam es to arabic nu m erals an d arabic n u m erals to w ritte n n u m b er nam es. (Deloche and Seron, 1982b an d Seron and Deloche, 1983). The authors concluded th at the patients' perform ance w as sim ilar w hatever the transcoding direction. The m ean overall error rate in both tasks was in fact about 27%. H ow ever, the authors did not present an error analysis on a subject by subject basis. Therefore, it rem ains questionable w hether an im pairm ent in tran sco d in g from verbal to arabic num erals is necessarily associated w ith an im p airm en t in transcoding from arabic to verbal num erals.

The aphasie patients w ere reported to com m it tw o types of qualitatively different transcoding errors. Broca's patients m ade p red o m in an tly stack errors, w h ile W ernicke's p a tie n ts m ad e p re d o m in a n tly errors of position in stack s tr u c tu r e s . These erro r ty p es correlated w ith the s v n ta c tic an d s e m a n t i c paraphasias m ade by these tw o types of aphasies in language tasks. This led the au th o rs to suggest a parallel betw een the dissolution of linguistic skills and the difficulties in num ber transcoding tasks. H ow ever, this particular conclusion can be questioned. It is well know n that syntactic p arap h asias can be d u e to lexical

deficits, loss of grammatical know ledge, or, as in the case of paragram m atism and o r d in a r y n o rm a l sp eech e rro rs , fro m tr a n s ie n t c o n tro l m a lfu n c tio n s (B utterw orth and H ow ard, 1987). It is well know n th at sem antic parap h asias can arise from im pairm ents w ithin the lexical sem antic com ponent as well as w ithin the o u tp u t lexicons (see for a detailed discussion, C aram azza an d Hillis, 1990). The stack errors and the errors o f position in stack stru ctu res c o u ld also p resu m ab ly come from deficits affecting different stages of th e transcoding system (for exam ple it w ould have been interesting to know the patients ability to co m p reh en d the to be tran sco d ed num eral). It is u nclear h o w w e should in te rp ret a correlation betw een im pairm ents that could have m u ltip le sources w ithin the inform ation processing system.

Deloche and Seron (1984a, b) proposed that som e specific verbal categories m ig h t share som e aspects of num ber class organization. The authors suggested th at the notion of stack structures could be applied also to ordinal dom ains other than the num ber dom ain, such as the nam es of the days in the week, the m onths in the year etc. For example, they reported the case of a deep dyslexic patient who m ad e paralexic errors such as saying January w hen trying to read M onday or Wednesday instead of March. They suggested that the stack notion perm its a re­ in te rp re ta tio n of "some sem antic confusions p articu larly b u t n o t exclusively those dealing w ith quantities".^