Investigating the Locus of the Word Frequency Effect in Spoken Word Recognition

Investigating the Locus of the Word Frequency Effect in Spoken Word Recognition Cynthia S. Q. Siew (cynsiewsq@gmail.com) Melvin J. Yap (melvin@nus.edu.sg) Winston D. Goh (psygohw@nus.edu.sg) Department of Psychology, National University of Singapore, 9 Arts Link, Singapore 117570, Singapore word recognition. With overwhelming evidence supporting both sides of the debate, the question as to whether word frequency affects spoken word recognition at an early or late stage continues. The present study aims to isolate the locus of the frequency effect in spoken word recognition by making use of the additive factors logic to investigate this particular research question. The additive factors logic (Sternberg, 1969) is widely used by cognitive psychologists to interpret RT data in factorial experiments and study the stages of processing in a number of research topics (e.g., Stanovich & Pachella, 1977), as the logic can be easily applied in the study a wide array of research topics, including psycholinguistics (e.g., Yap & Balota, 2007). Abstract The present study aims to isolate the locus of the frequency effect within the spoken word recognition architecture. By applying the additive factors logic (Sternberg, 1969) to an auditory lexical decision task where both word frequency and stimulus quality were factorially manipulated, the reaction time data can be analyzed to study processing stages along the time course of spoken word recognition, and determine if frequency has an early or late locus. A significant underadditive interaction of frequency and stimulus quality was obtained. Surprisingly, the typically robust frequency effect was not reliable for words of low stimulus quality. This finding suggests that word frequency influences a relatively late stage in the spoken word recognition process. Implications for extant models of spoken word recognition are discussed. Additive Factors Logic Keywords: Spoken word recognition; word frequency effects; stimulus quality effects; additive factors logic; auditory lexical decision. According to the additive factors logic (Sternberg, 1969), when two factors affect theoretically determined independent stages in the information processing stream, it should result in additivity in mean RTs (i.e., two main effects for each factor, but no interaction). This is represented in the top part of Figure 1, where Factor A affects processing at only Stage 1 and Factor B affects processing at only Stage 2. On the other hand, if the two factors affect the same stage in the information processing stream, this results in a statistical interaction (more precisely, an overadditive interaction where the effect of one factor is larger on the “slower” level of the second factor). This is depicted in the bottom part of Figure 1, where both Factor A and Factor B affect processing at a common Stage X. How can the incorporation of an additional variable, stimulus quality within the auditory lexical decision task, allow us to isolate the locus of the word frequency effect? How can the additive factors logic be used to help us make specific hypotheses about the pattern of results for RT data? In contrast to the lack of consensus with regards to the locus of the frequency effect, few would question the notion that stimulus quality has an early locus of influence in the word recognition process. In fact, a major assumption of most SWR models (e.g., TRACE) involves a process which converts physical, acoustic input into phonemic information (McClelland & Elman, 1986). This necessarily implies that degraded input must be normalized at a relatively early point in the word recognition process. Hence, if we assume that stimulus quality affects an early stage in the word recognition process, then Factor A corresponds to stimulus quality and Factor B corresponds to Introduction Determining whether word frequency has an early or late locus has profound theoretical implications for models of spoken word recognition (SWR). While it is well established that frequently occurring words are recognized faster than less frequently occurring words (Goldinger, 1996), what is less obvious is where the locus of the frequency effect lies within the word recognition process. Specifically, does frequency influence word recognition at an early stage, as the speech signal begins to unfold, or does frequency influence word recognition at a later stage in the form of a bias? Models of SWR can easily account for the frequency effect, but they do not necessarily agree on the locus of the frequency effect due to varying assumptions and architectures. Hence one way to test the validity of these models is to isolate the locus of the frequency effect. Several researchers have investigated this issue by employing a variety of experimental techniques and methodologies. Generally, studies which used traditional behavioral experiments (e.g., lexical decision and word identification) have demonstrated that word frequency has a late locus that occurs after lexical processes are complete (Broadbent, 1967; Connine, Mullennix, Shernoff & Yelen, 1990); Luce & Pisoni, 1998). On the other hand, recent studies employing eyetracking technology (e.g., Dahan, Magnuson & Tanenhaus, 2001) and novel behavioral applications of the parallel refractory period paradigm (Cleland, Gaskell, Quinlan & Tamminen, 2006) concluded that word frequency exerts early and facilitatory effects on