1. Neuro vs. Cognitive Psychology: A case study

2. Outline What is activation?- The view from fMRI The logic of subtraction Imaging orthographic similarity

3. Signs of activation Cellular activity in the brain is accompanied by: –Increased blood flow (and so temperature) in the activated area –Increased oxygen uptake in the activated area –Increased glucose use (during oxidative metabolism) –IF we can detect changes in blood flow or oxygen uptake or glucose metabolism or temperature, then we can deduce where cellular activity differences occur during any given task

4. Functional magnetic resonance imaging (fMRI) Measure ‘blood oxygen level dependent’ (BOLD) signal - increased local CBF during activity leads to excessive oxygenated hemoglobin (oxyhemoglobin) in that region (Anyone know why?) - Oxygenated and deoxygenated hemoglobin have different magnetic properties, the latter being magnetically charged - We can detect two different relaxation times: T1 (spin lattice relaxation time) and T2 (spin-spin relaxation time)- it is the latter that is used for functional imaging T2* is induced by local magnetic field homogeneity in the slice under current study fMRI resolution is about 1 X 1 x 3-4 mm.; temporal resolution is several seconds for whole brain

5. Subtraction logic Due to Donders, 1868 Let’s say you are interested in A Devise a task A+B, which incorporates A Ask subjects to do A+B and B alone –Then (A+B) - B = Time to do A –i.e. Color discrimination of lights - RT to lights = Color discrimination time

6. Subtraction logic Subtraction logic makes many assumptions, some of which are debatable The subtraction method necessarily or implicitly assumes: –that cognitive processing is serial –that cognitive processing is hierarchically organized –that cognitive processing unfolds in an exclusively forward fashion –that structures participate in an all or nothing fashion in a cognitive process

7. Subtraction logic in fMRI The subtraction method necessarily or implicitly assumes: –that peak CBF or glucose uptake or oxygen use corresponds to one single cognitive component of the task –that the same cognitive component of a task is always performed by the same brain region (and thus, implicitly, that the brain is not redundantly organized), even if that component is shared between different tasks –that subjects perform all and only the requested task (or that other tasks are are associated with random or perfectly consistent activity)

8. Subtraction logic None of the assumptions seems terribly likely, and several fly in the face of current theory about brain organization. What can we do to overcome doubt? Gather converging evidence.

9. Subtraction logic Subtraction logic is almost always used in imaging experiments –Recently, some have started using auto-correlation instead, but this is not wide-spread The nature and ‘purity’ of the subtraction is vital to interpretation of the imaging results For this reason, imaging results and experimental design are intimately and necessarily yoked

10. Language studies Language access is very fast & very complex, with multiple ‘micro-functional’ constraints – Experimental psycholinguistics has identified an over- whelming number of variables (several dozen) with demonstrable behavioral impact on lexical access = multiple ‘functional constraints’ in play There was a dissociation between early language imaging and psycholinguistic understanding, with stimuli in imaging studies failing to meet the rigourous control demands of psycholinguistic understanding

11. Micro-functional dissection Since even the simplest lexical access task is a multi-dimensional conglomeration of functionality, the key is to use very simple tasks, with very highly-controlled stimuli –In this way we try to ‘trap’ an automatic function of interest, well below conscious awareness –And we pray that it is fine-grained enough to be informative!

12. J.R. Binder, K.A. McKiernan, M.E. Parsons, C.F. Westbury, E.T. Possing, J.N. Kaufman, L. Buchanan (in press) Neural Systems Underlying Lexical Access During Word Recognition, Journal of Cognitive Neuroscience. ON

13. Coltheart’s Orthographic N [ON]: The number of words that are one-letter different from the target word -i.e. DOG ---> HOG, DOE, DOT, DIG etc. Many experiments manipulating ON have found a frequency-modulated neighborhood size effect. Uncommon words with large ON are recognized as words more rapidly than low-frequency words with small neighborhoods This effect disappears with common words This is among the bigger effects, with freq and ON together accounting for > 30% of variance in behavioral measures

15. Almost all words are uncommon.

16. The trap Task is lexical decision: decide whether or not a presented string is a word 50 high/low ON concrete nouns & nonwords (100 each in all) matched one-by-one on frequency, length, bigram frequency, and phonological neighborhood size, and (between wordness) on ON = the NWs are highly word-like, & the two real word sets are very similar to each other except for the manipulated ON

17. Hypotheses (i) Words should produce stronger activation than word-like nonwords in many of the brain regions previously identified in studies comparing semantic to non-semantic tasks, and (ii) A subset of these regions should show stronger responses to items with many lexical neighbors, indicating activation of pre-semantic word codes.

18. Behavioral data: RTs Psych Lab Scanner

19. Behavioral data: Errors Psych Lab Scanner

20. fMRI parameters GE Signa 1.5 Tesla scanner T1-weighted anatomical reference images: 124 contiguous sagittal slices (.9375 x.9375 x 1.2 mm) Functional imaging: 19 contiguous (7 - 7.5 mm) sagittal slice locations covering the entire brain x 3.75 x 3.75 mm 136 whole-brain image volumes collected from each subject at 2-sec intervals Each image was yoked to a behavioral decision (event- activated fMRI), allowing separate imaging of high/low ON x W/NW

21. Words vs NWs

22. Words - NWs

23. i.) Almost exclusively LH

24. Words - NWs ii.) Dorsal + inferior medial prefrontal activity

25. Semantic decision - phonological decision

27. Words - NWs iii.) Angular gyrus activity

28. Semantic decision - phonological decision

29. Transcortical sensory aphasia X -Damage to the ‘long route’ between Broca’s & Wernicke’s area -Main feature is a deficit in accessing (thinking about or remembering) the meanings of words - Comprehension is therefore severely impaired - The patient can neither read nor write and has major difficulty in word finding Lichtheim, 1885

30. Words - NWs iv.) Extensive midline activity

31. Words - NWs iv.) Extensive midline activity

32. High versus low ON

33. NW W Small ON [hard] - Large ON [easy]

34. i.) Small ON activation > Large ON activation We had (perhaps foolishly) hypothesized the opposite Although small ON is ‘harder’ by evidence of RT and error rates, high ON seems to coordinate a wider variety of information However: Greater constraints = Easier computation –Think of 20 questions after 19 questions have been asked

35. ii.) Bilateral midline activity The midline is not normally associated with lexical processing

36. ii.) Bilateral midline activity The midline is not normally associated with lexical processing –But we saw some in the W - NW contrasts:

37. ii.) Bilateral midline activity The midline is not normally associated with lexical processing –But we saw some in the W - NW contrasts: –And it was mirrored in the semantic tasks:

38. iii.) Words >> NWs There is almost no activity for the high - low ON condition for NWs NW

39. iii.) Words >> NWs There is almost no activity for the high - low ON condition for NWs What differentiates words from NWs? –Semantics! –By evidence of activation, ON manipulations are sensitive to semantics NW

40. ON vs [Semantics - phonology] W

41. ON vs Semantics W

42. Semantics as a ‘final push’ Small ON words seem to require more extensive semantic processing –Why? To compensate for the fact that these items are less orthographically word-like. High ON biases the subject toward a positive response (increases the tendency towards ‘yes’) –Relatively little semantic activation is then needed to complete the response selection task: hence [low ON - high ON] looks like [semantics - phonology] This explains why low ON > high ON, and why we don’t see the effects for NWs, which take the same semantic processing in both ON conditions

43. Why are high ON NWs slow and error-prone? Presumably high ON NWs are rejected more slowly and more likely to be accepted because of their greater resemblance to words = harder to reject However, the semantics interpretation fails: no NWs have any semantics And we cannot explain why there are (almost) no imagable effects of this very reliable behavioral difference, save some puzzling midline activity

44. Cognitive + Neuro psychology We probably would not (did not) have a view that ascribed semantic effects to ON sensitivity without imaging: Experimentation fails However, the only evidence we have (right now) of ON effects in NWs are robust experimental effects: Imaging fails It is a good thing that cognitive neuropsychology embraces both behavior and the brain

45. fin.