The purpose of the present study is to examine the nature of information that is available to the human sentence processing mechanism (i.e., the parser). We focus on the two types of information : “location information” and “grammatical information”. The experiment reported here was conducted in order to investigate which type of information is crucial for parsing two types of empty subject sentences: “subject-oriented” and “object-oriented” sentences. In a subject-oriented sentence such as “Taroo-ga Hanako-ni Tokyo iki-o hakuzyoosita (Taroo confessed to Hanako to go to Tokyo.)”, the person who will go to Tokyo is the subject “Taroo”. On the other hand, in an object-oriented sentence such as “Taroo-ga Hanako-ni Tokyo iki-o meireisita (Taroo ordered to Hanako to go to Tokyo)”, the object “Hanako” is supposed to go to Tokyo. Employing an on-line experimental technique (i.e., “dichotic listening” method), Oda et al. (1997) examined how the parser processes sentences such as the examples mentioned above. They found the “subject preference” phenomenon: the grammatical subject was preferred as the candidate for the empty subject of the embedded clause. However, no explanation was given for the reason of this outcome. Was the “preference” due to the “location” of the grammatical subject in the sentence initial position? Or, was the “preference” due to the grammatical subject bearing the grammatical function as the “subject”? In order to examine the word order effect, thus, we conducted an experiment employing the same procedure as that of Oda et al. except that the order of the subject and object in the sentence was exchanged. The results showed that, regardless of the change of the word order, there was the same “subject preference” effect that was observed in Oda et al. The findings of our experiment revealed that the surface order of the subject and object does not affect the tendency in which the grammatical subject is preferred as the candidate of the empty subject. This would suggest that the human parser does not make use of location information but rather makes use of grammatical information in sentence processing.
