Investigation of the neural correlates of time reference
Period: September 2010 - August 2014
Patients suffering agrammatic aphasia show problems with time reference expressed through verbs, as Bastiaanse found . The finding that reference to the past or future is more difficult than reference to the present led her to launch the Time Reference hypothesis (TRH) [1; 2], that says that time reference through grammatical morphemes is difficult to produce ánd understand for aphasic speakers, particularly when reference to the past should be made. There are several cross-linguistic studies that support the TRH, which relate to non-fluent as well as to fluent aphasia. TR difficulties have been reported for languages that differ structurally: both for languages with time reference expressed though verb inflection as through aspectual adverbs, such as Chinese and Indonesian [3-6].
A possible cause of time reference problems is the anaphoric nature of time reference. For past, the anaphor refers back to a point in time earlier than the here and now of the moment of speaking, so to a preceding time frame. For future, the anaphoric reference cannot be made, because the moment to which is referred is in a time-frame that does not exist yet. For present, the anaphoric reference is to the current time frame, resulting in the least cognitive load since no access to another time frame is needed.
This anaphoric nature of time reference processing is believed to be demanding for patients with agrammatic aphasia, taking their limited working memory into account. Making grammaticality judgments on sentences with time reference violations by anomalous tense marking has shown to be difficult for agrammatic speakers . Answering occurs at chance level. The semantic and syntactic properties of the sentence as a whole might cause too much processing cost and distraction to correctly carry out the task of judging whether tense is violated or not. Using a more fine-grained technique — for example the ERP-technique — can reveal whether the aphasic brain notices the time reference violations. If so, some of the mechanisms necessary for time reference processing are still present in patients, but cannot be used properly because of compromised cognitive resources.
A core issue in neurolinguistics is the question to what extent language problems that people with aphasia experience are characteristic of the impaired brain and not reflected in the healthy brain. Results on an ERP-experiment and a subsequent reaction time (RT) experiment with written stimuli [7; 8] indicate that also in non-brain-damaged people differences in time reference processing of past versus present can be found. The results suggest that directly upon reading a present tense verb, the temporal characteristics are extracted from the tense inflection and compared to the temporal context. When this morphosyntactic operation results in a violation, this is reflected in a P600-effect . Contrastively, a verb referring to the past is not integrated into the temporal context of the sentence straight away. This was reflected in a longer RT and the absence of a P600-effect in response to the ungrammaticality caused by verbs referring to the past as compared to verbs referring to the present. When the sentence is finished this entails for both violation conditions that the semantic mismatch between time reference of the adverb and verb (still) cannot be solved, resulting in an N400-effect [10; 11].
At least partially different brain regions are activated during sentence comprehension for auditory and reading tests . Most aphasia data on the comprehension of time reference were collected using auditory stimuli, while the study described in the previous paragraph [7, 8] used visual stimuli. Whether auditory and visual time reference are nevertheless processed in the same way has not been investigated yet. Also, so far, no study has been performed that investigates the activation networks of time reference. Because of its anaphoric nature, past time reference is likely to evoke more brain activation or different activation patterns than present time reference.
The project will focus on the anaphoric nature of time reference, both in the brain of healthy people as in the impaired brain of patients suffering aphasia. For this, a comparison with other anaphoric constructions (pronouns, reflexives, Wh-question words) will be made. Methods include neuro-imaging and behavioural experiments. Most of the experiments will be carried out in Dutch.
The project is funded by the CLCG (Center for Language and Cognition, Groningen)
 Bastiaanse, R. (2008) Production of verbs in base position by Dutch agrammatic speakers: Inflection versus finiteness. Journal of Neurolinguistics, 21, 104-119.
 Yarbay Duman & Bastiaanse (2009). Time reference through verb inflection in Turkish agrammatic aphasia. Brain & Language, 108, 30–39.
 Jonkers, R. & Bruin, A. de (2009). Tense processing in Broca’s and Wernicke’s aphasia. Aphasiology, 23, 1252-1265.
 Anjarningsih, H.Y., Bamyaci, E., Hsu, C.-J. & Bastiaanse, R. (2009). The comprehension of time reference in agrammatic aphasia: A comparison of languages with Tense and languages with aspectual adverbs. Paper presented at the Science of Aphasia X, Antalya, Turkey.
 Stavrakaki, S., & Kouvava, S. (2003). Functional categories in agrammatism: Evidence from Greek. Brain and Language, 86, 129–141.
 Faroqi-Shah, Y. & Dickey, M. W. (2009). On-line processing of tense and temporality in agrammatic aphasia. Brain & Language, 108, 97–111.
 Bos, L.S. (2010) Time Reference in non-brain-damaged and agrammatic speakers of Dutch, studied with ERPs and grammaticality judgment. Unpublished Master’s thesis, University of Potsdam, Germany/University of Groningen, The Netherlands.
 Dragoy, O., Bos, L. S., Stowe, L.A. & Bastiaanse, R. (in preparation) Time reference processing studied with ERP. To appear in NeuroImage.
 Friederici, A. D. (2002). Towards a neural basis of auditory sentence processing. Trends in Cognitive Sciences, 6, 78-84.
 Kutas, M. & Hillyard, S. A. (1980) Reading senseless sentences: brain potentials reflect semantic anomaly. Science, 207, 203–205.
 Kutas, M. & Hillyard, S. A. (1983). Event-related brain potentials to grammatical errors and semantic anomalies. Memory & Cognition , 11, 539–550.
 Friederici, A. D. (2002). Towards a neural basis of auditory sentence processing. Trends in Cognitive Sciences 6, 78-84.