Characteristics of Forgetting Functions in Delayed Matching to Sample

Abstract

Performance of pigeons in delayed matching-to-sample procedures was measured in terms of an index of discriminability derived from the difference between logarithms of ratios of choice responses to comparison stimuli following the different sample stimuli. Forgetting functions that plotted discriminability as a function of delay-interval duration were well described by a simple negative exponential function with two parameters, one describing initial discriminability of sample stimuli at zero delay (log do) and the other describing rate of decrement in discriminability with increasing delay-interval duration (b). With the difference between wavelength values of the comparison stimuli held constant, a large difference between wavelengths of the sample stimuli resulted in a higher log do value than that for a small difference between sample stimuli, without changing the rate of decrement in discriminability, b. An increase in the fixed-ratio requirement for sample-key responding produced an increase in log do without affecting b, and interpolation of ambient illumination in the delay interval increased b without influencing log do. Both parameters changed when intertrial-interval duration was varied. The result of variation in the point of interpolation of ambient illumination in the delay interval indicated that levels of discriminability at longer delays were independent of discriminability levels at earlier delays, consistent with the properties of the exponential function. Functions relating performance to delay-interval duration were suggested to have two characteristics: discriminability of the sample stimuli in the absence of a delay between the stimuli and the behavior they occasion, and rate of attenuation in discriminability with increasing delay-interval duration.

Forgetting functions

“…An entire forgetting function in which performance may vary considerably over a wide range of retention intervals can be summarized in terms of the parameters of a fitted function (White, 1985). By fitting negative exponential functions to a set of data from studies of animal memory, White (1985White ( , 1991 concluded that forgetting functions have two characteristics that could be captured by the two parameters of the fitted function.…”

“…By fitting negative exponential functions to a set of data from studies of animal memory, White (1985White ( , 1991 concluded that forgetting functions have two characteristics that could be captured by the two parameters of the fitted function. The first characteristic is initial discriminability, or accuracy at t 5 0, given by the value of the intercept.…”

“…The first characteristic is initial discriminability, or accuracy at t 5 0, given by the value of the intercept. White (1985) interpreted the intercept as reflecting the effects of attentional demands or overall procedural requirements in the absence of a memorial requirement. In the animal studies, factors that render the short-term memory task more difficult result in a reduction in discriminability or accuracy at t 5 0, without affecting the slope parameter of the fitted function (White, 1985).…”

“…White (1985) interpreted the intercept as reflecting the effects of attentional demands or overall procedural requirements in the absence of a memorial requirement. In the animal studies, factors that render the short-term memory task more difficult result in a reduction in discriminability or accuracy at t 5 0, without affecting the slope parameter of the fitted function (White, 1985). Such factors include decreasing the disparity between stimuli to be remembered, decreasing the number of repetitions of a stimulus on initial presentation, or decreasing the trial separation.…”

“…When the negative exponential function was fitted to a set of data from animal working memory studies, rate of forgetting varied with factors related to retroactive interference and proactive interference, without influencing the value of the intercept parameter (Edhouse & White, 1988;Jones & White, 1994;White, 1985White, , 1991. White and Harper (1996) used the exponential to Öt function to satisfactorily fit a large set of data pertaining to the effects of hippocampal lesions in monkeys.…”