On the discriminability of stimulus duration.

The performance of pigeons trained to detect differences in the duration of stimuli was analysed using a matching model of signal detection. Two white stimuli, S1 and S2, differing in duration, were arranged with equal probability on the center key of a three-key chamber. S1 was systematically varied from 5 seconds to 25 seconds while S2 remained constant at 30 seconds. On completion of the center-key stimulus, a peck on the center key turned on the two red side keys. A left-key response was "correct" when S1 had been in effect on the center key and a right-key response was "correct" on S2 trials. A correct response produced a 3-second magazine light accompanied intermittently by food. Incorrect responses produced 3-second blackouts. Detection performance was measured under two procedures. In the first, the obtained reinforcement ratio was uncontrolled by allowing the number of food reinforcements obtained for correct left- and right-key responses to vary as the stimuli were changed. In the second procedure, the presentation of food reinforcement was controlled by holding the obtained reinforcement ratio constant. Discriminability changed as a function of stimulus differences under both procedures. No such trend was found in response bias.     

Local contrast in multiple schedules: the effect of stimulus discriminability.

A three-ply multiple schedule assessed responding in a standard component as a function of the just-preceding schedule. The principal experimental condition was the difference among the wavelengths signaling the schedule components. Only the pigeons working in a narrow wavelength range showed persistent positive local contrast; that is, response rate during the standard component was higher when that component followed extinction than when it followed itself. Birds in both narrow- and medium-range groups showed persistent negative local contrast; that is, rate was lower following a relatively rich component. The dissipation of positive contrast appeared to be most clearly related to the establishment of differential responding. Negative contrast was inversely related to wavelength differences. Theories pertaining to contrast must account for the role of discrimination in both positive and negative types.     

Independence of stimulus discriminability from absolute rate of reinforcement in a signal-detection procedure.

Three experiments are reported in which two pigeons were trained to detect differences in stimulus duration under varying levels of absolute rate of reinforcement. Two red stimuli, differing in duration, were arranged probabilistically on the center key of a three-key chamber. On completion of the center-key duration, the center keylight was extinguished and the two side keys were illuminated white. Correct responses were left-key pecks following the shorter duration and right-key pecks following the longer duration. In Experiment 1, relative rate of reinforcement for correct responses was held constant and absolute rate of reinforcement was varied in seven conditions from continuous reinforcement to a variable-interval 90-second schedule. In Experiment 2, relative rate of reinforcement was manipulated across three different absolute rates of reinforcement (continuous reinforcement, variable-interval 15-second, and variable-interval 45-second). Stimulus discriminability was unaffected by changes in absolute or relative rates of reinforcement. Experiment 3 showed that discriminability was also unaffected by arranging the same consequences (three-second blackout) for unreinforced correct responses and errors.     

Delayed reinforcement and delayed choice in symbolic matching to sample: Effects on stimulus discriminability

Six pigeons were trained to peck a red side key when the brighter of two white lights (S₁) had been presented on the center key, and to peck a green side key when the dimmer of two white lights (S₂) had been presented on the center key. Equal frequencies of reinforcers were provided for the two types of correct choice. Incorrect choices, red side-key pecks following S₂ presentations and green side-key pecks following S₁ presentations, resulted in blackout. With 0-s delay between choice and reinforcement, the delay between sample presentation and choice was varied from 0 to 20 s. Then, with 0-s delay between sample presentation and choice, the delay between choice and reinforcement was varied from 0 to 20 s. Both types of delay resulted in decreased discriminability (defined in terms of a signal-detection analysis) of the center-key stimuli, but delayed choice had more effect on discriminability than did delayed reinforcement. These data are consistent with the view that the two kinds of delay operate differently. The effect of a sample-choice delay may result from a degradation of the conditional discriminative stimuli during the delay; the effect of a choice-reinforcer delay may result from a decrement in control by differential reinforcement.     

Dimensional stimulus control following brief wavelength training

Pigeons with extensive training pecking a key illuminated by a white line then had brief training with the key illuminated by 555 nanometers. This was immediately followed by a wavelength generalization test in extinction. Dimensional stimulus control about the training wavelength increased with the duration and number of reinforcements given on variable-interval 30-sec and variable-interval 10-sec schedules in Experiment I. In Experiment II, dimensional stimulus control was obtained after only 4 min of wavelength training from birds with prior and independent discrimination training. Experiment III provided groups equated in number of reinforcers with groups in Experiment I and two 8-min duration groups. Analyses, which included results from both Experiments I and III, showed that dimensional stimulus control increased: (a) more rapidly as a function of the duration of variable-interval 10-sec than variable-interval 30-sec reinforcement; (b) at the same rate across variable-interval reinforcement schedules, as a function of the number of reinforcers available during brief wavelength training.     

视听刺激突显性对视觉主导效应的影响

本研究使用空间任务-转换范式,控制视、听刺激的突显性,探讨自下而上注意对视觉主导效应的影响。结果表明视、听刺激突显性显著地影响视觉主导效应,实验一中当听觉刺激为高突显性时,视觉主导效应显著减弱。实验二中当听觉刺激为高突显性并且视觉刺激为低突显性时,视觉主导效应进一步减弱但依然存在。结果支持偏向竞争理论,在跨通道视听交互过程中视觉刺激更具突显性,在多感觉整合过程中更具加工优势。     

The discriminability of smooth stereoscopic surfaces.

In this study the sensitivity of human vision to the smoothness of stereoscopic surface structure was investigated. In experiments 1 and 2 random-dot stereograms were used to evaluate the discrimination of smooth versus 'noisy' sinusoidal surfaces differing in the percentages of points on a single smooth surface. Fully coherent smooth surfaces were found to be much more discriminable than other less smooth randomly perturbed surfaces. In experiment 3 the discrimination between discontinuous triangle-wave surfaces and similarly shaped smoothly curved surfaces obtained from the addition of the fundamental and the third harmonic of the corresponding triangle-wave surface was evaluated. The triangle-wave surfaces were found to be more accurately discriminated from the smoothly curved surfaces than would be predicted from the detectability of the difference in their Fourier power spectra. This superior discriminability was attributed to differences between the curvature and/or discontinuity of the two surfaces. In experiment 3 the effects of incoherent 'noise' points on the discrimination between the two surface types were also evaluated. These randomly positioned noise points had a relatively small effect on the discrimination between the two surfaces. In general, the results of these experiments indicate that smooth surfaces are salient for stereopsis and that isolated local violations of smoothness are highly discriminable.     

Stimulus discriminability in free-operant and discrete-trial detection procedures.

Six pigeons were trained to discriminate different light intensities in four experimental procedures. Experiment 1 compared stimulus discriminability in a yes-no signal-detection task with discriminability measures obtained from two free-operant procedures. Discriminability estimates were significantly lower in the detection procedure. Experiment 2 showed this lowered discriminability to be a function of the delay between stimulus presentation and the availability of the choice-response keys in the standard detection task. In addition, reinforcement sensitivity was lowest when correct choice responses were intermittently, rather than continuously, reinforced.     

Effect of stimulus opening size in global dominance with orientation classification task

The aims of this study is to examine whether global dominance depends on the opening size of the stimulus with concentric hierarchical figures and orientation classification task and to determine the role of the salience of global opening and its coincidence with vertical symmetry axis of context. In the first experiment, participants had to indicate the opening direction of stimuli, which were open-left and open-right figures. Three openings were included: 10, 25 and 50% of the total circle perimeter. The results showed a local advantage with stimuli of 10%, absence of global or local advantage with stimuli of 25% and global advantage with stimuli of 50%. In the second experiment, stimuli with an opening of 50% were presented randomly in several positions in the visual field in order to avoid the coincidence of global opening with the vertical symmetry axis of context. The results showed an absence of global or local advantage. These findings indicate that global dominance with orientation classification task depends on stimulus characteristics such as opening size, and strategies used in visual recognition.     

Viewpoint dependence and object discriminability

In an attempt to reconcile results of previous studies, several theorists have suggested that object recognition performance should range from viewpoint invariant to highly viewpoint dependent depending on how easy it is to differentiate the objects in a given recognition situation. The present study assessed recognition across depth rotations of a single general class of novel objects in three contexts that varied in difficulty. In an initial experiment, recognition in the context involving the most discriminable object differences was viewpoint invariant, but recognition in the least discriminable context and recognition in the intermediate context were equally viewpoint dependent. In a second experiment, utilizing gray-scale versions of the same stimuli, almost identical viewpoint-cost functions were obtained in all three contexts. These results suggest that differences in the geometry of stimulus objects, rather than task difficulty, lie at the heart of previously discrepant findings.     

Duration comparison: relative stimulus differences stimulus age, and stimulus predictiveness.

Under a psychophysical trials procedure, pigeons were presented with a red light of one duration followed by a green light of a second duration. Eight geometrically spaced base durations were paired with one of four shorter and four longer durations as the alternate member of a duration pair, with different pairs randomly intermixed. One choice was reinforced if red had lasted longer than green, and a second choice was reinforced if green had lasted longer. Performance was compared when all the base durations and their pair members were included (entire-range condition) or when only the four longest base durations and their comparison durations (restricted-range condition) were used. Discrimination sensitivity decreased for longer duration pairs under both conditions, supporting a memory-based account. Sensitivity was lower under the restricted-range condition. Under both conditions, a bias to report "green as longer" increased as the second green duration increased. Bias changed as a matching function of the green-duration predictiveness of the correct choice. The results are related to a quantitative model of timing and remembering proposed by Staddon.