Commas and Spaces: The Point of Punctuation

While it has been widely assumed that punctuation may play a critical role in parsing, there has been relatively little direct empirical investigation of its effects. Most researchers have either avoided the use of punctuation or have simply assumed that it will serve a disambiguating role. There has been little or no consideration of how ’disambiguation’ might occur or whether it is equally effective across different structures. Previous work using selfpaced reading (Hill & Murray, 1997) has in fact shown that simplistic conclusions related to the role of punctuation are unlikely to be supported. These studies showed that while punctuation can play a potent disambiguating role in some structures, the effect is by no means universal. These conclusions, however, depend on the assumption that punctuation acts in the same way with word-by-word self-paced reading as it does in more natural reading tasks. The studies reported here therefore extended this work by the monitoring of subjects’ eye movements while reading three types of locally ambiguous items with and without inserted punctuation. Since results from an earlier pilot study showed effects of punctuation on saccade length, an additional condition of increased spacing, without punctuation, was also included. The results showed potent effects of punctuation on first pass ’garden pathing’ in two structures (early closure and reduced relative clause sentences), but not in sentences with prepositional phrase ambiguities. Punctuation also had effects on local processing difficulty, suggesting that it can cue some types of parsing decision at particular points in a sentence. A frequent effect of inserted punctuation was to increase processing time on sections of a sentence immediately preceding a comma, while facilitating processing which followed. Punctuation and increased spacing between words had similar effects on saccade length into a region, increasing these by more than the added character space, but while spacing manipulations did impinge on reading time, they did not have an equivalent disambiguating effect. Punctuation therefore appears to convey information related to structure that is more potent than the simple ’chunking’ of text, but this effect is limited to particular structural conditions. Interestingly, there was little effect of punctuation when it was consistent with a ’preferred’ parse. Its role appears to be more closely related to the avoidance (in some circumstances) of incorrect decisions.