CONTEXT EFFECTS IN THE PERCEPTION OF SENSORY MAGNITUDE

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DESCRIPTION (From the application): "Sensory judgements are subject to various well-known effects of stimulus context. For instance, a solution of sodium chloride at 0.1 M concentration may be related as "strong" in the context of NaC of lower concentrations but as "weak" in the context of greater ones. It is widely assumed that the sensory processing underlying the perception of the 0.1 M NACl is the same in both situations, only that the judgement changes. But not all effects of context necessarily reflect processes of judgement alone. Of special theoretical importance are newly-discovered differential context effects. Here, responses to one kind of stimulus can marked markedly relative to responses to another kind of stimulus. For example, interspersing strong sodium chloride solutions with weaker sucrose solutions make the salt taste weaker; interspersing intense high- pitched tones and weaker low-pitched tones makes the high-pitched tones sound softer. Considerable evidence suggests, though does not prove, that these differential context effects largely reflect sensory changes and not judgmental bias. The proposed research is guided by the hypothesis that differential context effects resemble the sensory "adaptation" or "fatigue" produced by prolonged intense stimulation but depend on a distinct underlying mechanism. To test this hypothesis, experiments will first seek to show that the effects are sensory by decoupling sensory and decisional processes. This will be done by measuring response speed and accuracy. Then, experiments will compare relative threshold and suprathreshold responses after exposure to transient versus long-duration stimuli in order to test the hypotheses that, unlike adaptation produced by prolongation intense stimulation, differential context produced by a small number of brief stimulations (a) involve central neural processes; (b) are smaller at threshold than at suprathreshold levels; (c) show proportional attenuation of sensation whereas adaptation shows recruitment-like growth of sensation magnitude; and (d) exert effects specific to the configural properties common to the exposure and test stimuli. These experiments will examine differential context effects in several modalities: taste, hearing (loudness), touch (vibrotaction), and vision (perceived lengths). Differential context effects appear to be widespread and potent sensory phenomena, albeit ones that have receive little prior recognition; consequently, delineating the underlying mechanisms is central to understanding basic sensory processes."