Academic journal article Canadian Journal of Experimental Psychology

Stimulus Modality and Stimulus-Resonse Compatibility in Absolute Identification

Academic journal article Canadian Journal of Experimental Psychology

Stimulus Modality and Stimulus-Resonse Compatibility in Absolute Identification

Article excerpt

Abstract Accuracy and response time (RT) were measured in the absolute identification (AI) of ten unidi-mensional perfectly pairwise discriminable stimuli. One group of 20 subjects performed a visual AI task involving line segments of variable length. A second group of 20 subjects participated in an auditory task with the stimuli composed of pure tones of variable intensity. Subjects performed the task under two conditions: a spatially compatible and a spatially incompatible stimulus-response mapping. Results showed greater accuracy for the visual modality and longer RT for the incompatible mapping. The experimental factors did not substantially alter the bowing observed when performance was plotted according to the ordinal position of the stimuli. The data do not support the hypothesis that the bow effect is attributable to motor programming or motor adjustment stages. Absolute identification (AI) tasks involve a set of n stimuli which vary according to a physical characteristic such as the length of line segments in the case of visual absolute identification, or intensities of pure tones of fixed frequencies in auditory absolute identification. Generally, the range of values lies along a unidimensional continuum, and stimuli are perceptually equidistant. In a commentary on capacity limitations, Shiffrin and Nosofsky (1994) have emphasized the intriguing and yet not well explained fact that performance in absolute identification is greatly limited. Subjects are usually unable to maintain perfect performance in unidimensional AI tasks if the experiment involves more than seven stimuli. This performance limitation corresponds to approximately 2.5 bits of transmitted information and is observed even when pairwise discrimination among stimuli is perfect. Furthermore, increasing the stimulus range or the amount of practice generally leads to only slight improvements in performance (e.g., Braida & Durlach, 1972; Shiffrin & Nosofsky, 1994). A robust phenomenon in AI is the bow effect (also know as the 'edge' or 'end' effect). The bow effect consists of a performance deterioration as the set size increases, with stimuli located toward the ends of the stimulus range being identified with greater accuracy than those located in the middle of the continuum. Although at first one might suggest that this effect is due to response biases or limited response alternatives toward the ends of the range, several researchers have concluded that the effect is due to poorer sensitivity at the ends of the range (e.g., Berliner, Durlach, & Braida, 1977; Braida & Durlach, 1972; Luce, Nosofsky, Green, & Smith, 1982). Durlach and Braida (1969) and Gravetter and Lockhead (1973) suggested that absolute identification is based on scale values in which the variance of the stimulus representation is proportional to the square of the signal range. Concluding that range alone is not sufficient to explain performance limitation, Berliner and Durlach (1973) subsequently proposed that the end stimuli are used as anchors or comparison points, and that stimuli further away from the anchors are associated with higher variance. Thus, performance limitation is attributed to the number of stimuli represented in the psychological space and the bowing in accuracy is attributed to the relative distance of each stimulus representation from the anchor points. The anchor hypothesis was later formally stated by Marley and Cook (1984) and Braida, Lim, Berliner, Durlach, Rabinowitz, and Purks (1984). The mathematical formulations allow for precise predictions of accuracy based on stimulus range and ordinal position. Luce, Green, and Weber (1976) developed another explanation for performance limitations in AI. They postulated a selective attention mechanism called the attention band and hypothesized that, on each trial, subjects tended to focus their attention in the area of psychological representation where the previous stimulus was represented. Such an attention mechanism would, in part, explain the bow effect. …

Search by... Author
Show... All Results Primary Sources Peer-reviewed

Oops!

An unknown error has occurred. Please click the button below to reload the page. If the problem persists, please try again in a little while.