A Study Of The Effect Of Unknown Vocabulary Density On Efficiency Of Incidental Vocabulary Acquisition From Second Language Reading

Incidental vocabulary acquisition from second language reading has always beenan important aspect that Second Language Acquisition (SLA) studies are preoccupiedwith, and the density of unknown words is assumed to be a significant factorinfluencing the incidental vocabulary acquisition from reading, some studies argue thatthe density of unknown words accounts for the variance of pickup rate among studiesinvestigating incidental vocabulary acquisition from reading. It is argued that when thedensity of unknown words of a reading material is high, due to the dissipation ofattention of learners and the reduction of contextual support, incidental vocabularyacquisition can hardly be effective; when the density of unknown words is low, owingto the scarcity of new words contained in the material, incidental vocabulary is alsoexpected to be lowly efficient. It is thus widely accepted that the optimum density ofunknown words that prompts incidental vocabulary growth from reading should be setwithin an intermediate range, e.g.2%-5%, this argument, however, has not yet beenvalidated by empirical evidence.This study explored the efficiency of vocabulary growth in both the short and longterm resulted from different densities of unknown words through an experiment, inwhich materials of4densities of unknown words (2%,4%,6%,8%) were read by4groups of subjects of the same level, in the hope of providing empirical evidence forvalidating the argument that optimum density of unknown words should be set withinan intermediate range, as well as providing learners with a means to choose appropriatereading materials for growing vocabulary effectively.Results of the experiment show that the4%experiment group gained the highestefficiency of vocabulary growth among the4groups in both immediate test and delayedtest, suggesting that4%is a density appropriate to incidental vocabulary acquisitionfrom reading. The6%group presented a decent performance in immediate test, onlybehind4%group in terms of efficiency of vocabulary growth, however, in the delayedtest, efficiency of6%group declined greatly and fell behind2%group, suggesting thatfor long-term retention of vocabulary learnt through reading, the density range of2%~4%might be superior to that of4%~6%.