Reinforcer Control by Comparison‐stimulus Color and Location in a Delayed Matching‐to‐sample Task

Abstract

Six pigeons were trained in a delayed matching-to-sample task involving bright-and dim-yellow samples on a central key, a five-peck response requirement to either sample, a constant 1.5-s delay, and the presentation of comparison stimuli composed of red on the left key and green on the right key or vice versa. Green-key responses were occasionally reinforced following the dimmer-yellow sample, and redkey responses were occasionally reinforced following the brighter-yellow sample. Reinforcer delivery was controlled such that the distribution of reinforcers across both comparison-stimulus color and comparison-stimulus location could be varied systematically and independently across conditions. Matching accuracy was high throughout. The ratio of left to right side-key responses increased as the ratio of left to right reinforcers increased, the ratio of red to green responses increased as the ratio of red to green reinforcers increased, and there was no interaction between these variables. However, sidekey biases were more sensitive to the distribution of reinforcers across key location than were comparison-color biases to the distribution of reinforcers across key color. An extension of Davison and Tustin's (1978) model of DMTS performance fit the data well, but the results were also consistent with an alternative theory of conditional discrimination performance (Jones, 2003) that calls for a conceptually distinct quantitative model.

Remembering and forgetting.

“…The absence of bias at long delays means that the reinforcer proportion remains at its arranged value, typically 0.5, and the discrimination is not influenced by fluctuations in reinforcer proportions. Attempts to control the reinforcer proportion (McCarthy & Davison, 1991) can result in large reductions in the levels of obtained reinforcers at long delays and large bias for other dimensions of the choice between comparison stimuli (Alsop & Jones, 2008;Brown & White, 2009a;Jones & White, 1992;White & Wixted, 1999). Inclusion of a very short delay at all stages of training minimizes response bias at medium and long delays (White, 1985).…”

Matching-to-sample performance is better analyzed in terms of a four-term contingency than in terms of a three-term contingency

“…With regard to issues, treating a difference between C 1 and C 2 selection frequencies as response bias renders ambiguous the interpretation of any tendency to emit left responses more often than right responses (or vice versa) in MTS tasks where trial scheduling ensures that the two positions are correct equally often. Position biases have varied systematically with manipulations of reinforcement variables (e.g., Alsop & Jones, 2008; Jones, 2003; Jones & White, 1992; Katz, 1989; McCarthy & Davison, 1991) and often appear early in MTS training (Cumming & Berryman, 1965; Jackson & Pegram, 1970; Kangas & Branch, 2008). Some researchers have considered them a second type of response bias (Brown & White, 2009; Katz, 1989; Nevin & Grosch, 1990) but BDTs do not accommodate position bias despite it having implications for bias-free measures of stimulus control (Brown & White, 2009).…”