Structural and Strategic Factors in the Stimulus Suffix Effect

The stimulus suffix effect has been typically viewed as reflecting the displacement of the current information residing in a limited-capacity sensory store by the presentation of a subsequent speech sound. The present research was primarily concerned with determining if strategic factors will also influence the stimulus suffix effect. An experiment was conducted, based on the research by Aaronson (Journal of Experimental Psychology, 1968, 76, 129-140; Cognitive Psychology, 1974, 6, 133-158), in which both presentation rate (6, 3, 1.5 digits/second) and practice with suffix or no-suffix lists were factorially crossed betweensubjects factors. The serial recall results of 7-item lists of digits indicated that both presentation rate and practice with suffix lists modulated the preterminal suffix effect for serial positions 3 -6 , whereas, the terminal suffix effect for serial position 7 was relatively unaffected by these variables. These results were viewed as indicating that the suffix effect reflects two distinct processes: 1) a more strategic mechanism which primarily underlies the preterminal suffix effect and 2) a more structural mechanism which primarily underlies the terminal suffix effect. It was therefore argued that only the terminal suffix effect should be viewed as a relatively pure index of the contribution of echoic information to short-term memory performance.