Discrete and continuous measures of dimensional stimulus control

Range effects in transient and maintained generalization gradients

In three experiments pigeons were trained to discriminate visual flicker rate stimuli. The stimulus set was varied so that the effects of overall stimulus range and border separation between positive and negative stimuli could be assessed. Experiments 1 and 2 showed that transient generalization gradients were lower in height and flatter with increases in either border separation or overall stimulus range. Border separation and overall range interacted in that the effect of range was greatest with relatively greater border stimulus separation. Experiment 3 showed that increased overall stimulus range reduced the magnitude of positive dimensional contrast in maintained gradients. Flattening of the maintained gradient with increases in stimulus range was similar to flattening of post-discrimination gradients found in Experiments 1 and 2. The results from all experiments indicate that increases in overall stimulus range do not decrease discriminability of unchanged stimulus values. Instead, increases in stimulus range may increase the variability of response or criterial factors in discrimination.

Métodos de pesquisa em análise do comportamento

Apresenta-se neste artigo a discussão sobre o status da análise do comportamento como disciplina científica, bem como sua relação com outras ciências e as implicações desta discussão para a caracterização dos métodos de pesquisa em análise do comportamento. Várias classificações dos métodos de pesquisa são apresentadas, com destaque para o método experimental, tendo em vista seu papel na construção da disciplina. Os supostos e as principais características dos delineamentos de sujeito único são apresentados. E, por fim, são brevemente discutidas algumas questões que se originam da interação e aparente confronto entre conceituação e prática de pesquisa em análise do comportamento, tais como: reversibilidade comportamental, variabilidade comportamental, procedimentos de tentativa e procedimentos de operante livre, análise molecular e análise molar, tratamento estatístico e quantificação, pesquisa experimental com humanos.

Adaptation level effects in discrimination of flicker frequency

Pigeons accustomed to food reinforcement for responding in the presence of a 25-Hz flickering light were exposed to several sets of flicker-frequency stimuli arranged as increasing and decreasing series. In the first experiment, food was occasionally delivered for key pecks during 30-s periods of 25-Hz flicker appearing at the beginning, midway, and at the end of an ascending and descending series of nine frequencies, ranging from 13 to 37 Hz. These stimuli appeared for 15-s periods with no food available (extinction). Gradients of responding to flicker values in the ascending series differed from those in the descending series, showing displacements in peak responding toward the lower and higher frequency values, respectively. The same effects occurred when the sequence was changed so that a descending series was followed by an ascending series of frequencies. These effects are consonant with an adaptation level (AL) interpretation and were replicated in a second experiment in which durations of the extinction presentations were increased to 30s. In a final condition, only a descending series was presented and displacement of peak responding from 25 Hz to a higher frequency stimulus, 28 Hz, was observed.

Patterns of responding within sessions

Rates of responding changed systematically across sessions for rats pressing levers and keys and for pigeons pressing treadles and pecking keys. A bitonic function in which response rates increased and then decreased across sessions was the most common finding, although an increase in responding also occurred alone. The change in response rate was usually large. The function relating responding to time in session had the following general characteristics: It appeared early in training, and further experience moved and reduced its peak; it was flatter for longer sessions; and it was flatter, more symmetrical, and peaked later for lower than for higher rates of reinforcement. Factors related to reinforcement exerted more control over the location of the peak rate of responding and the steepness of the decline in response rates than did factors related to responding. These within-session changes in response rates have fundamental theoretical and methodological implications.