Logical and pragmatic inferencing abilities afterleft- and right-hemisphere lesions

Caroline Hamel a,b,*, Yves Joanette a,c

a Centre de recherche, Institut universitaire de geriatrie de Montreal, Canadab Departement de Psychologie, Universite de Montreal, Canada

c Faculte de medecine, Universite de Montreal, Canada

The ability to infer new information is a central component of dis-course comprehension. Readers or listeners must make inferences to inte-grate sentences in a coherent fashion and fill in anything that is missing orambiguous in the discourse (Singer, 1994). Inferencing processes have beenstudied most in the context of right-hemisphere-damaged (RHD) partici-pants because text-level processes are probably subserved by right-hemi-sphere structures (Ferstl & von Cramon, 2001).

Although several types of inferences have been described (Singer,1994), two are particularly important for discourse and pragmatic abilities(Harris & Monaco, 1978) and will be considered here: logical and prag-matic inferences. Logical inferences, or syllogisms, are based on formalrules. They require the integration of two premises in order to infer anew relationship. On the other hand, pragmatic inferencing abilitiesrequire a set of cognitive operations that are partially or totally basedon the individual’s general knowledge of the world (Singer, 1994).

Although many studies have investigated the inferencing abilities ofRHD adults, few have tried to compare their abilities with those of left-hemisphere-damaged (LHD) adults. The goal of this study is to explorethe impact of left- and right-hemisphere lesions on the inferencing abilitiesof adults, and to explore the possibility of individual differences in bothpopulations.

Materials and methods

Participants

Seventy-two right-handed (more than +80 on the Edinburgh Handed-ness Inventory, Oldfield, 1971) native French-speakers participated in thisstudy: 30 RHD, 14 LHD and 28 control participants matched as a groupfor age and education. None of the participants had a previous history ofpsychiatric or neurological disease or brain injury. None of the RHD orLHD participants had cognitive deficits (e.g., neglect or aphasia) thatwould have interfered with the proposed tasks.

Materials

Forty short syllogisms were used for the logical inferencing task. Eachsyllogism was constructed using two premises followed by a question. Dif-ferent levels of difficulty were established according to the spatial arrange-ment of the syllogisms (De Soto, London, & Handel, 1965), theirmarkedness and their congruency (Clark, 1969). For the pragmatic infer-encing task, participants heard a short story (200 words), followed by 30YES/NO statements (10 false, 10 true and 10 requiring an inference).

Procedure

Each participant performed the two tasks individually. All stimuli werepresented in a pseudo-randomized order. In order to eliminate any mem-ory effect, the material remained available to the participants until theygave their answers.

Results (see Table 1)

A cluster analysis (Clustan Graphics, 2002) was done on the perfor-mance of all participants together for both tasks. For the logical infer-

encing task, the results suggest the existence of three sub-groups. Sub-group 1 performs better as a whole, has the highest level of educationand is, not surprisingly, composed mainly of controls and LHD sub-jects. Sub-group 2 has only 11 members, who have the lowest perfor-mance scores and the lowest level of education; this group has 23.3%of the RHD participants. Sub-group 3’s performance and educationlevel are located between those of sub-groups 1 and 2; it has a largeproportion of RHD participants (50%). For the pragmatic inferencing

task, the results indicate four different sub-groups. This time, half ofthe RHD subjects are found in sub-group 2, with few LHD or controlsubjects, and medium performance scores. The best performance scoresare achieved by sub-group 3, which has the largest total number of par-ticipants and the largest proportion of controls.

Discussion

The results of this study first show that both a right- and a left-hemi-sphere lesion can affect individuals’ ability to process logical or pragmatic

doi:10.1016/j.bandl.2007.07.036

* Corresponding author.E-mail address: caroline.hamel@umontreal.ca (C. Hamel).

www.elsevier.com/locate/b&l

Brain and Language 103 (2007) 8–249

inferences. However, this study shows the heterogeneity among brain-damaged participants and suggests that RHD, unlike LHD participants,have significant problems resolving inferences. There is probably morethan one cause of a deficit affecting inferencing abilities; moreover, itmay represent a contributing factor and not the sole cause of the prag-matic difficulties experienced by some brain-damaged individuals. It isimportant to consider these results in the clinical evaluation and manage-ment of brain-damaged individuals.

References

Clark, H. H. (1969). Linguistic processes in deductive reasoning. Psycho-

logical Review, 76, 387–404.

De Soto, C. B., London, M., & Handel, S. (1965). Social reasoning andspatial paralogic. Journal of Personality and Social Pathology, 2,513–521.

Ferstl, E. C., & von Cramon, D. Y. (2001). The role of coherence andcohesion in text comprehension: An event-Related fMRI study.Cognitive Brain Research, 11, 325–340.

Harris, R. J., & Monaco, G. E. (1978). The psychology of pragmaticimplication: Information processing between the lines. Journal of

Experimental Psychology: General, 107, 1–22.Oldfield, O. D. (1971). The assessment and analysis of handedness: The

Edinburgh Inventory. Neuropsychologia, 9, 97–113.Singer, M. (1994). Discourse inference processes. In M. A. Gernsbacher

(Ed.), Handbook of psycholinguistics (pp. 479–515). San Diego, CA:Academic Press.

Table 1Cluster data for logical and pragmatic inferencing tasks

Sub-groups Logical inferencing task Pragmatic inferencing task

1 2 3 1 2 3 4

Number of members in the cluster 33 11 28 5 18 35 14% of RHD in the cluster/

total number of RHD26.67 23.33 50.00 10.00 50.00 30.00 10.00

% of LHD in the cluster/total number of LHD

50.00 7.14 42.86 0 14.29 57.14 28.57

% of controls in the cluster/total number of controls

64.29 10.71 25.00 7.14 3.57 64.29 25.00

% of right answers (SD) 86.15 (9.64) 32.95 (9.28) 63.84 (9.59) 69.33 (5.479) 75.56 (10.97) 93.43 (4.08) 73.33 (9.15)Mean age in years (SD) 61.43 (14.25) 63.64 (11.54) 63.22 (12.31) 76.40 (10.92) 60.83 (11.18) 61.15 (13.62) 64.71 (11.80)Mean years of education (SD) 10.72 (3.74) 7.82 (2.75) 8.29 (3.18) 5.75 (1.893) 8.56 (3.87) 10.27 (3.65) 9.20 (2.14)

44 Abstract / Brain and Language 103 (2007) 8–249