Frost, Ram

Keuleers, Emmanuel

English

Ghent University Academic Bibliography

What can we learn from monkeys about orthographicprocessing in humans?A reply to Ziegler et al.Ram Frost The Hebrew UniversityHaskins LaboratoriesThe Basque Center on Cognition Brain and LanguageAndEmmanuel KeuleersGhent UniversityWord-count: 872Through  two  provocative  papers  (Grainger  et  al.,  Science,  2012;  Ziegler  et  al.,Psychological  Science, in  press),  six  baboons  have  recently  become  unexpectedcontributors to reading research. The baboons were trained using operant conditioningto  differentiate  between  repeated  four-letter  “word”  stimuli  with  high-frequencyEnglish  bigrams,  such  as  DONE,  and  four-letter  “nonword”  stimuli  with  low-frequency bigrams,  such  as  VIRT.  The  papers  report  that  the  baboons  learned todiscriminate  the  words from the nonwords with  relatively  high-accuracy,  and likehumans they also showed transposed-letter  effects  (the baboons tended to confusenonwords as  belonging to  the  “word”  category  they had been trained on,  if  theyinvolved letter transpositions (DNOE-DONE). The authors argue that since baboonsdo not  have a linguistic  system, but  nevertheless perform like humans,  the neuralmechanisms underlying orthographic processing in the two species must be similarand therefore nonlinguistic. We will  argue that  these conclusions are logically fallacious and do not withstandempirical scrutiny. If performance of baboons with printed material is at all similar tothat of humans, it does not follow that the neural mechanisms underlying orthographicprocessing  of  humans  is  similar  to  that  of  baboons.  Similarly,  the  presence  oftransposed-letter effects  in  the  absence  of  a  linguistic  system does  not  imply  theabsence  of  linguistic  modulation  of  transposed-letter effects.  More  importantly,however, close inspection reveals that the baboons’ behavior as reported by Ziegler etal., is critically different from that of humans.The issue at stake is the extent to which humans and baboons respond similarly tomisspellings of words that contain transposed letters. Studies that have examined theimpact of manipulating letter-order on reading performance in humans have shown asmall cost of letter-transpositions in terms of reading time, along with robust maskedpriming effects when primes and targets share all of their letters but in a differentorder (e.g., Perea & Lupker, 2003). In their recent paper, Ziegler et al. have shownthat the six baboons classify both words (DONE) and their transposed letter version(DNOE) as “words”. While at first glance, this finding may seem to be similar to thatof  humans,  Ziegler  et  al.  seem  to  forget  that  the  transposed  letter  phenomenonpresupposes a substantial  ability to differentiate words from their transposed letterversions in the first place. Considering the baboons absolute level of accuracy, theyseem to consistently perceive the transposed-letter versions as “words”, making asmany positive responses to trained words as they make false positive responses totransposed letter nonwords. This stands in sharp contrast to humans who correctlyreject transposed letter nonwords in a lexical decision task (albeit more slowly andslightly less accurately than nonwords with substituted letters, e.g., Chambers, 1979).Thus,  humans  have  a  genuine  flexibility  in  coding letter  position  in  spite of  theexplicit knowledge that letter-order matters in constructing words. For now, the onlything that has been shown is that baboons have learned that the presence of certainshapes or symbols in a series has a relation to a particular response category, and thatthe order in which they are presented does not matter. This does not mean that theydemonstrated “flexible” letter-coding. Moreover, as Ziegler et al. report, the baboonscould not discriminate between “words” and nonwords that were one-letter different,again  in  sharp  contrast  to  humans.  This suggests that a  critical  proportion  ofmismatches  is  required  for  two  series  of  shapes  to  be  considered  different  forbaboons, demonstrating severe limitations on how far “orthographic processing” candevelop non-linguistically via the object recognition system. Ziegler et al., also seemto  forget  that transposed-letter  effects  for  humans are not  always present,  and aremodulated by the linguistic properties of the stimuli (e.g., Dunabeitia et al., 2012, seeFrost  2012a,b,  for  a  review).  Baboons  by  definition  are  blind  to  such  linguisticfactors. Comparing abilities of humans and non-humans allows us to trace the demarcationline between processing mechanisms shared  with  other  species  and those  that  arespecifically human. However, such investigations should also seek the point at whichperformance of  species  diverges,  rather  than halt  at  an apparent  convergence.  Forexample,  finding that  both  humans  and  rats  can  segment  a  stream of  continuousspeech (e.g., Toro & Trobalon, 2005) does not imply that the cues that govern speechsegmentation  are  identical  for  humans  and  rats.  Indeed  Toro  and  Trobalondemonstrate  that  rats  are  sensitive  to  simple  frequency of  co-occurrence,  whereashumans  rely  on  transitional  probabilities.  Returning  to  “reading”  performance  ofbaboons the results simply show that baboons can learn probabilistic conjunctions of3-4 individual shapes, and that this learning does not extend to the order of the shapes.Whether this form of statistical learning should be labeled “orthographic processing”seems very doubtful.  More important,  the data  regarding how letter  transpositionsaffect  baboons  vs.  how  they  affect  humans,  certainly  does  not  suggest  that  theprocessing mechanisms for orthographic information are the same in the two species.The inevitable conclusion is, therefore, that the recent findings with baboons revealsomething about their statistical learning abilities, but have no important implicationsfor theories of human visual word recognition.  Acknowledgement:  This paper was supported by the ISF (Grant 159/10 awarded to Ram Frost), and by the NICHD (RO1 HD067364 awarded to Ken Pugh and Ram Frost, PO1HD 01994 awarded to Haskins Laboratories). ReferencesChambers, S.M. (1979). Letter and order information in lexical access.  Journal ofVerbal Learning and Verbal Behavior, 18, 225-241.Duñabeitia,  .A.,  Dimitropoulou,  M, Grainger,  J.,  Hernández,  J.A,  & Carreiras,  M.(2012).  Differential  sensitivity  of  letters,  numbers,  and symbols  to  charactertransposition. Journal to Cognitive Neuroscience, 24, 1610-1624.Frost,  R.  (2012a).  Towards  a  universal  model  of  reading.  Behavioral  and  BrainSciences, 35, 263-280.Frost R. (2012b). A universal model of reading: not only possible but also inevitable.Behavioral and Brain Sciences, 35, 310-321. Grainger, J., Dufau, S., Montant, M., Ziegler, J. C. & Fagot, J. (2012) Orthographicprocessing in baboons (Papio papio). Science, 336, 245–48. Perea, M., & Lupker, S. J. (2003). Transposed-Letter Confusability Effects in MaskedForm Priming. In S. Kinoshita & S. J. Lupker (Eds.), Masked priming: the stateof the art (pp. 97-120). New-York: Psychology Press.Toro, J.M., & Trobalon, J.B. (2005). Statistical computations over a speech stream ina rodent. Perception & Psychophysics, 67, 867-875.Ziegler, J.  C., Hannagan, T., Dufau, S.,  Montant, M., Fagot,  J., & Grainger, J.  (inpress). Transposed Letter Effects Reveal Orthographic Processing in Baboons.Psychological Science.

What can we learn from monkeys about orthographic processing in humans? A reply to Ziegler et al.

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What can we learn from monkeys about orthographic processing in humans? A reply to Ziegler et al.

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