This study addressed the potential methodological issues effect of attentional condition on subsequent vocabulary development from a different perspective, which addressed several potential methodological issues of previous research that have been based on psycholinguistic notion of second language learner as a limited capacity processor. The issue of whether learners paying attention to the processing of input for meaning can simultaneously pay attention to process form remains methodologically unclear issue in the area of reactivity. A qualitative study was conducted on six intermediate English as a foreign language learners. Participants were assigned to one of the three types of reading comprehension tasks. Concurrent data of think aloud was employed to establish learners' attention. Results showed that attending learners' attention to processing of lexical forms while reading for meaning has an effect to induce the issue of reactivity effect on subsequent vocabulary development.