Academic journal article The Psychological Record

Effects of Successive and Simultaneous Stimulus Presentations on Absolute and Relational Stimulus Control in Adult Humans

Academic journal article The Psychological Record

Effects of Successive and Simultaneous Stimulus Presentations on Absolute and Relational Stimulus Control in Adult Humans

Article excerpt

Stimuli have multiple properties, and responding has the potential to be controlled by one or more properties of a stimulus but not others. One well-known distinction in how stimulus control is expressed is that of absolute stimulus control versus relational stimulus control. Absolute control is when responding depends on some intrinsic characteristic of a stimulus. For example, if the stimulus of interest is a line of particular length, absolute control would be evinced by a pattern of responding to lines of a matching length (or similar lengths due to stimulus generalization). Relational control is when responding is controlled by a relative characteristic of a stimulus. For example, in the case of line lengths, responding might occur in the presence of all relatively long lines.

Research on absolute and relational stimulus control spans decades, and within this literature much of the concern has been with the factors affecting the acquisition of a particular form of control (e.g., Hauf, Prior, & Sarris, 2008; Lazareva, 2012; Moll & Nieder, 2014; Reese, 1968; Riley, 1968; Wills & Mackintosh, 1999). A subject that has been little explored, especially with normally functioning adult humans, concerns which form of control will prevail in situations that allow either form of control to be expressed, and the reasons why one form of control should take precedence over another in those situations. Consider the typical methods used to study peak shift and stimulus transposition. In both cases, participants first receive discrimination training with one stimulus paired with reinforcement (S+) and a second stimulus paired with the absence of reinforcement (S-). For example, S+ might be a 10-cm-long line, and S- a 7-cm-long line. Participants may perceive that S+ has both absolute characteristics (it is 10 cm in length) and relational features (it is relatively long), but the procedure does not allow them to determine which feature makes S+ the line that should be selected. The methods used to study peak shift and stimulus transposition both include a test of stimulus control that encompasses a wider variety of stimuli (in the example, the test would include a wider variety of line lengths). At times, the test forces participants to express only one form of control. That is, participants might respond whenever a line is shown that appears to match S+ in length (thus evincing absolute control), or they might respond to all line lengths that match the relative difference between the stimuli (thus evincing relational control), but they cannot consistently do both. Participants do not receive feedback after making a response. Therefore, the tasks can be viewed as a vehicle for exploring participants' tendency toward absolute and relational stimulus control in what is (from the participant's perspective) a somewhat ambiguous situation (cf. Johnson & Zara, 1960).

A key procedural detail that has been omitted so far concerns how the stimuli are presented. In the case of research on peak shift, it is customary to present a single stimulus on each training and testing trial, while in the case of research on stimulus transposition, it is customary to present two stimuli on each trial. Although participants might perceive that S+ has absolute and relative features under either method, the stimulus presentation mode nevertheless appears to be important. Studies of peak shift characteristically produce absolute stimulus control, and studies of transposition characteristically produce relational stimulus control. Possibly the manner in which stimuli are presented to participants is the single most important factor determining which form of stimulus control is expressed (more on this below).

Evidence for absolute control in research on peak shift comes from the distribution of responses emitted during the test. Typically, this distribution takes the form of a generalization gradient with a peak (or modal response) centered on one test stimulus (see Fig. …

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