Journal of Experimental Psychology: Human Perception and Performance 1995, Vol. 21, No. 3, 512-530 Copyright 1995 by the American Psychological Association, Inc. 0096-1523/95/S3.00 Perceiving Exterior Letters of Words: Differential Influences of Letter-Fragment and Non-Letter-Fragment Masks Timothy R. Jordan University of St. Andrews Previous research shows letter-fragment masks and non-letter-fragment fields have different effects on performance with briefly presented alphabetic targets. However, popular accounts of these differences ignore mask configuration. Over a series of experiments, configurational effects of letter-fragment (LF) and non-letter-fragment (NLF) masks were compared. When the configuration of LF masks matched word boundaries, performance with exterior letter pairs from words improved, whereas performance with illegal exterior-letter pairs and single letters was unaffected. When the same changes were made to NLF masks, only an overall drop in performance occurred, with no selective effect on target type. Thus, although LF mask configuration selectively affected lexical processing, NLF mask configuration produced substantially different effects, indicating problems with contemporary accounts of masking differences that ignore influences of mask configuration. Since Cattail's early studies (Cattell, 1886), examinations of the perceptibility of briefly presented alphabetic stimuli have provided valuable insight into the process of visual word recognition. In particular, by severely limiting the amount of time for which an alphabetic target (e.g., word, nonword, single letter) is presented, information can be gained to determine which physical characteristics of words are encoded by the reader and over what time scale this encoding takes place. Naturally, research in this area has concentrated on the role played by the characteristics of each type of alphabetic target (see McClelland & Rumel- hart, 1981, and Henderson, 1987, for reviews). However, many researchers have also studied the role played by each posttarget field, and the different patterns of performance produced by different types of posttarget stimulus have become a critical means of revealing the processes respon- sible for visual word recognition (e.g., Johnston, 1981; Johnston & McClelland, 1973, 1980; Jordan, 1990; Jordan & Bevan, 1994a, 1994b; Jordan & de Bruijn, 1993; Juola, Leavitt, & Choe, 1974; Marchetti & Mewhort, 1986; Mas- saro & Klitzke, 1979; McClelland & Rumelhart, 1981; Taylor & Chabot, 1978; Turvey, 1973). A substantial body of research into the effects of posttar- get stimuli on performance indicates that masks composed This research was supported by Grant SPG 8931914 from the Joint Council Initiative in Cognitive Science. Preliminary aspects of this research were reported at the meeting of the Experimental Psychology Society, University of Cambridge, Cambridge, En- gland, April 1991. I am grateful to Phil Allen, Dave Bohnsack, Hannah Buchanan- Smith, Ken Forster, James Johnston, and Greg Stone for useful comments concerning various aspects of this work. Correspondence concerning this article should be addressed to Timothy R. Jordan, Psychological Laboratory, University of St. Andrews, St. Andrews, Fife KY16 9JU Scotland. Electronic mail may be sent via Internet to trj@st-andrews.ac.uk. of irregular arrangements of letter fragments (or similar contours) affect performance with different types of alpha- betic target in ways that are not observed when posttarget stimuli devoid of letter fragments are used. For example, when studying the relative perceptibility of words and iso- lated letters under forced-choice conditions, several studies have shown that performance is better for words than for isolated letters when targets are followed by a letter-frag- ment mask (the word-letter effect; e.g., Johnston & McClel- land, 1973; Jordan & Bevan, 1994a, 1994b; Jordan & de Bruijn, 1993; Marchetti & Mewhort, 1986; Massaro & Klitzke, 1979; Reicher, 1969; Taylor & Chabot, 1978). However, when words and isolated letters are followed by a plain posttarget field in which no letter fragments or similar contours are present, the advantage for words disappears (e.g., Johnston & McClelland, 1973; Marchetti & Mewhort, 1986; Massaro & Klitzke, 1979; Taylor & Chabot, 1978). Furthermore, although word advantages over nonwords have been observed with both letter-fragment masks and non-letter-fragment fields, this word—nonword effect is gen- erally more substantial when letter-fragment masks are used. For example, Massaro and Klitzke (1979) obtained a word-nonword effect of just 4% when a non-letter-fragment field was used but a word-nonword effect of 12% when targets were followed by a letter-fragment mask. 1 These contrasting effects of letter-fragment masks and non-letter-fragment fields on the relative perceptibility of alphabetic targets have inspired the popular notion that 1 The precise nature of letter-fragment and non-letter-fragment posttarget stimuli varies across different studies. For example, the non-letter-fragment posttarget stimuli used in many studies were bright flashes of white light (often called energy masks), whereas some studies used dark posttarget fields. However, the presence or absence of letter fragments (or similar contours) in the posttarget field remains the critical difference relevant to current theoretical concerns, and it is this difference that forms the focus of the present study. 512