Timing the second response in two-response avoidance.

Rats were trained on a free-operant avoidance task requiring two lever presses within R seconds, with the opportunity for each response distinguished by differing stimuli. Response latencies at a variety of response-shock intervals were found to be proportional to the time available for the response. These results are shown to be consonant with a scalar expectancy model of timing behavior.     

Pavlovian contingencies and temporal information

The effects of altering the contingency between the conditioned stimulus (CS) and the unconditioned stimulus (US) on the acquisition of autoshaped responding was investigated by changing the frequency of unsignaled USs during the intertrial interval. The addition of the unsignaled USs had an effect on acquisition speed comparable with that of massing trials. The effects of these manipulations can be understood in terms of their effect on the amount of information (number of bits) that the average CS conveys to the subject about the timing of the next US. The number of reinforced CSs prior to acquisition is inversely related to the information content of the CS.     

Using image analysis techniques to analyze figure-copying performance of patients with visuospatial neglect and control groups

Figure copying is often used to detect visuospatial neglect (VSN) in brain-damaged patients. We describe algorithms that enable the computation of parameters for describing figure-copying performance. The researcher can readily implement these algorithms on a computer using image analysis software, and they provide information on goodness-of-fit, relative to a standard model, as well as on dynamic aspects of subjects’ performance in completing figure copies. To demonstrate the clinical utility of these algorithms, preliminary results from a group of right-hemisphere brain-damaged patients, some of whom have VSN, are compared with those for age-matched controls.     

Ratio versus difference comparators in choice.

Several theories in the learning literature describe decision rules for performance utilizing ratios and differences. The present paper analyzes rules for choice based on either delays to food, immediacies (the inverse of delays), or rates of food, combined factorially with a ratio or difference comparator. An experiment using the time-left procedure (Gibbon & Church, 1981) is reported with motivational differentials induced by unequal reinforcement durations. The preference results were compatible with a ratio-comparator decision rule, but not with decision rules based on differences. Differential reinforcement amounts were functionally equivalent to changes in delays to food. Under biased reinforcement, overall food rate was increased, but variance in preference was increased or decreased depending on which alternative was favored. This is a Weber law finding that is compatible with multiplicative, scalar sources of variance but incompatible with pacemaker rate changes proportional to food presentation rate.     

Scalar Timing in Animals and Humans

John Gibbon's lifetime work provided a deep understanding of the mechanisms whereby the time sense indexes the passage of time (its accumulation) and records, that is, stores, relevant time intervals in memory, enabling behavior to occur at the right time. The Scalar Expectancy Theory (SET; Gibbon, 1977) remains the most prominent of the theoretical accounts of animal and human timing. SET deals with the three principle psychophysical properties of timing data: flexible accuracy, multiplicative variance, and ratio comparisons. It differs from many other timing theories in its emphasis on scalar variability, a term that refers to the linear increase in the standard deviation of timing errors as a task's criterion time increases. Recently, research based on the conceptual framework and analytic tools of SET in John Gibbon's lab was expanded from a decades-long focus on nonhuman species to an assessment of timing performance in “normal” and brain-diseased human subjects, aimed at understanding the functional and neural mechanisms underlying interval timing in humans. This review is aimed at showing that animal and human data obtained with a variety of timing paradigms are both amenable to analyses of accuracy and scalar variability under the SET framework. In the second part of this report we discuss advances made in our understanding of neurobiological mechanisms underlying interval timing by taking advantage of the SET framework. Issues awaiting new theoretical developments in modeling time production and perception, as revealed by psychophysical findings of recent clinical research that are still not well understood (i.e., sources of nonscalar variability), are raised at the end.     

The Ethical Subject and Willing Subject in the Tractatus: an Alternative to the Transcendental Reading

Philosophia - The Transcendental Reading of the Tractatus argues that Wittgenstein endorses, under the notion of ‘metaphysical subject’, the existence of a willing subject as a...     

Correction to: The Ethical Subject and Willing Subject in the Tractatus: an Alternative to the Transcendental Reading

Philosophia - The original version of the article missed to include an acknowledgments. The missing information is provided below.     

Using image analysis techniques to analyze figure-copying performance of patients with visuospatial neglect and control groups.

Figure copying is often used to detect visuospatial neglect (VSN) in brain-damaged patients. We describe algorithms that enable the computation of parameters for describing figure-copying performance. The researcher can readily implement these algorithms on a computer using image analysis software, and they provide information on goodness-of-fit, relative to a standard model, as well as on dynamic aspects of subjects' performance in completing figure copies. To demonstrate the clinical utility of these algorithms, preliminary results from a group of right-hemisphere brain-damaged patients, some of whom have VSN, are compared with those for age-matched controls.     

Conditioned stimulus informativeness governs conditioned stimulus-unconditioned stimulus associability

In a conditioning protocol, the onset of the conditioned stimulus ([CS]) provides information about when to expect reinforcement (unconditioned stimulus [US]). There are two sources of information from the CS in a delay conditioning paradigm in which the CS-US interval is fixed. The first depends on the informativeness, the degree to which CS onset reduces the average expected time to onset of the next US. The second depends only on how precisely a subject can represent a fixed-duration interval (the temporal Weber fraction). In three experiments with mice, we tested the differential impact of these two sources of information on rate of acquisition of conditioned responding (CS-US associability). In Experiment 1, we showed that associability (the inverse of trials to acquisition) increased in proportion to informativeness. In Experiment 2, we showed that fixing the duration of the US-US interval or the CS-US interval or both had no effect on associability. In Experiment 3, we equated the increase in information produced by varying the C/T ratio with the increase produced by fixing the duration of the CS-US interval. Associability increased with increased informativeness, but, as in Experiment 2, fixing the CS-US duration had no effect on associability. These results are consistent with the view that CS-US associability depends on the increased rate of reward signaled by CS onset. The results also provide further evidence that conditioned responding is temporally controlled when it emerges.     

Temporal landmarks: proximity prevails

Subjects in conditioning experiments time their conditioned responses relative to the onsets of the conditioned stimuli (CSs). These onsets are temporal landmarks, by reference to which subjects may estimate the location of the unconditioned stimulus (US) in time. In a serial compound conditioning paradigm, a long duration CS comes on first, followed later by a second shorter CS, creating both a long-range and a short-range predictor of the US. We ask whether displacing the short-range predictor relative to the long-range predictor causes subjects to strike a compromise between the different temporal locations predicted by the two CSs. In three experiments with pigeons, we varied the training conditions so as to favor or militate against this outcome. However, in all conditions, there was no compromise; after the onset of the displaced short-range CS, the timing of conditioned responding was governed by it alone. This result contrasts with the compromises that are seen when the feeding time predicted by a CS is put in conflict with the time predicted by the circadian clock, and with the similar compromises sometimes seen when a nearby spatial landmark is displaced relative to a larger spatial context. Electronic Publication