A simple,all-mechanical operant apparatus

An apparatus is described that utilizes the force exerted by a rat in turning a wheel to rotate reward cups into his presence after passing through a reservoir containing water or ground mash. The response-ratio requirement, force requirement, and amount of reward can be manipulated by simple adjustment or interchange of parts.     

Variation of Isometric Response Force in the Rat

Hungry, unrestrained rats (N = 7) were rewarded for pressing a response beam in excess of 11 different force requirements. Changes in peak force production as a function of peak force requirement were examined by analyses of the first four moments of distributions of peak response forces: constant error, the within-subject standard deviation, skewness, and kurtosis. Results were similar to those previously obtained with human subjects: Constant error was positive at low and negative at high force requirements, the within-subject standard deviation increased as a negatively accelerating function of force requirement, and skewness and kurtosis were positive at low force requirements and decreased to negative values at the highest increments. Additional analyses of response kinetics indicated that rats, like humans, meet increasing force requirements by altering the rate of rise of force. The performance similarities suggest that common processes are engaged by the human and rat motor control systems to solve the problem of generating forces that are appropriate to the prevailing environmental constraints.     

Effect of drugs on response-duration differentiation VII: response-force requirements

Rats were trained to press a lever for at least 1 s but for less than 1.3 s. The force required to press the lever was then increased or decreased by 10, 15, or 20 g. Increases in the force requirements for lever pressing decreased timing accuracy, but decreases in the force requirement had the opposite effect. Accuracy decreases at increasing force requirements were characterized by an increase in the relative frequency of responses that were too short to meet the reinforcement criterion. In contrast, increases in accuracy when the force requirements were decreased were characterized by increases in response durations that met the reinforcement criterion and decreases in the relative frequency of responses that were too short to produce the reinforcer. Phencyclidine (PCP) and methamphetamine produced dose-dependent decreases in accuracy that were associated primarily with increases in the relative frequency of short response durations, although methamphetamine also produced increases in long response durations at some doses. When the effects of PCP were determined with the force requirement increased by 10 g or decreased by 15 g, the cumulative response-duration distribution shifted toward even shorter response durations. When the effects of methamphetamine were determined with the force requirement on the lever increased by 10 g, the cumulative frequency distribution was shifted toward shorter response durations to about the same extent as it had been before force requirements increased; however, when the force required to press the lever was decreased by 15 g, these shifts toward shorter response durations almost completely disappeared. These results show that increases and decreases in the force requirements for lever pressing have different effects on the accuracy of temporal response differentiation.     

Variation of Isometric Response Force in the Rat

Hungry, unrestrained rats (N = 7) were rewarded for pressing a response beam in excess of 11 different force requirements. Changes in peak force production as a function of peak force requirement were examined by analyses of the first four moments of distributions of peak response forces: constant error, the within-subject standard deviation, skewness, and kurtosis. Results were similar to those previously obtained with human subjects: Constant error was positive at low and negative at high force requirements, the within-subject standard deviation increased as a negatively accelerating function of force requirement, and skewness and kurtosis were positive at low force requirements and decreased to negative values at the highest increments. Additional analyses of response kinetics indicated that rats, like humans, meet increasing force requirements by altering the rate of rise of force. The performance similarities suggest that common processes are engaged by the human and rat motor control systems to solve the problem of generating forces that are appropriate to the prevailing environmental constraints.     

Aquinas and Luther on War and Peace: Sovereign Authority and the Use of Armed Force

Recent just war thought has tended to prioritize just cause among the moral criteria to be satisfied for resort to armed force, reducing the requirement of sovereign authority to a secondary, supporting role: such authority is to act in response to the establishment of just cause. By contrast, Aquinas and Luther, two benchmark figures in the development of Christian thought on just war, unambiguously gave priority to the requirement of sovereign authority as instituted by God to carry out the responsibilities of ensuring a just and peaceful order in the world. On this conception it is the sovereign, in deciding whether to resort to armed force, who must make sure to satisfy the other moral requirements of the jus ad bellum . This paper examines Aquinas and Luther on sovereign authority for use of armed force. Recapturing the importance of this conception is important both for the proper understanding of just war tradition and for working out its implications for such contemporary issues as humanitarian intervention and "regime change."     

Independence of response force and reinforcement rate on concurrent variable-interval schedule performance

Five pigeons were trained over 43 experimental conditions on a variety of concurrent variable-interval schedules on which the forces required on the response keys were varied. The results were well described by the generalized matching law with log reinforcement ratios and log force ratios exerting independent (noninteractive) effects on preference. A further analysis using the Akaike criterion, an information-theoretic measure of the efficiency of a model, showed that overall reinforcement rate and overall force requirement did not affect preference. Unlike reinforcement rate changes, force requirement increases did not change the response rate on the alternate key, and an extension of Herrnstein's absolute response rate function for force variation on a single variable-interval schedule is suggested.     

Learned helplessness in the rat: time course, immunization, and reversibility.

Rats, like dogs, fail to escape following exposure to inescapable shock. This failure to escape does not dissipate in time; rats fail to escape 5 min, 1 hr., 4 hr., 24 hr., and 1 wk. after receiving inescapable shock. Rats that first learned to jump up to escape were not retarded later at bar pressing to escape following inescapable shock. Failure to escape can be broken up by forcibly exposing the rat to an escape contingency. Therefore, the effects of inescapable shock in the rat parallel learned helplessness effects in the dog.     

The effects of differing response types and price manipulations on demand measures

Animals' behavioral needs have become an important component of animal welfare legislation. Behavioral economics provides a framework for the study of such needs. A function, analogous to a demand function relating consumption rate to price, can be obtained by increasing the price (or work) required for access to a commodity. This experiment investigated the effects of different response types and price manipulations on these functions. Six hens pushed a door or pecked a key for food under open economic conditions (short experimental sessions and supplementary food). In Part 1, the number of door pushes required (fixed-ratio schedule) was increased each session, and the force needed to push the door was increased across conditions. In Part 2, the force needed to push the door was increased session to session, and the fixed-ratio schedule was increased across conditions. In Part 3, the number of key pecks required was increased each session. Both response types produced similarly shaped (approximately linear in logarithmic coordinates and downward sloping) demand functions when price was increased by increasing the number of responses required. These imply an elastic demand for food under these conditions. In contrast, increasing the force required to push the door resulted in highly curvilinear functions. These functions indicated little change in consumption across lower door forces and abrupt drops in consumption at higher force requirements, implying mixed elasticity in the animals' demand for food. The differences between the shapes of the two functions seem to arise from the different ways that the two price manipulations alter the time taken to complete the work required. Increasing the fixed-ratio requirement necessarily increases the time needed to complete each response unit, whereas increasing the force requirement does not. The different shapes of the functions were robust when either force or number was varied across sessions and the value of the other was varied over conditions. They were also robust when the price increases were taken from different conditions, showing that the shapes of the functions were independent of the place in the experiment in which the price was examined. Unit price (which combines number and force into a single price measure) unified the data from the two price manipulations to a large degree, producing moderately curved functions. However, there was some variance around the unit price functions, and this was attributable to the different shapes of the underlying functions. The data suggest that different price manipulations may give different measures of animal demand but that unit price might provide some unification.     

Effects of differing response-force requirements on food-maintained responding in CD-1 mice

The effect of force requirements on response effort was examined using outbred (CD-1) mice trained to press a disk with their snout. Lateral peak forces greater than 2 g were defined as threshold responses (i.e., all measured responses). Different force requirements were used to define criterion responses (a subclass of threshold responses) that exceeded the requirement. The reinforcer was sweetened, condensed milk, and it was delivered upon response termination. All mice were exposed to two ascending series of criterion force requirements (2, 4, 8, 16, and 32 g). Increasing the force requirement decreased criterion response rates, but increased threshold response rates. The time-integral of force (area under the force-time curve for individual responses, which is proportional to energy expenditure for each response) increased with the increase in the force requirement. These results conflict with the hypothesis that higher force requirements have aversive qualities and suggest that increased force requirements are more analogous to intermittent schedules of reinforcement. These data suggest that estimations of effort or energy expenditure should be measured independently of the force requirement. Individual differences in responding were found for the CD-1 outbred stock.     

Some punishing effects of response-force

The present experiment explored the punishing effect of different response-force requirements by means of a two-operant design analogous to a two-component chain schedule. The first component of the chain required a lever pull through 0.25 in. (0.64 cm) at 1 lb (4.45 N) of force. The second component required a lever pull through an additional 0.75 in. (1.90 cm) with the force varied between sessions from 1 lb to 50 lb (4.45 N to 223 N). Completion of the second component of the chain was reinforced after variable intervals averaging 1 min. The average rate of first-component response decreased as the force requirement for second-component responses was increased. This rate reduction did not appear to be due to increased response duration, “fatigue”, or differing rates of reinforcement. If the force requirement for the second-component response is viewed as a consequence for the first-component response, then the results of the experiment show that a high force requirement is a punisher.     

The physical properties of bar-pressing behaviour and the problem of reactive inhibition

Many of the terms used in the literature on reactive inhibition are vague, subjective or incorrect. The weighted bar is not a suitable device in the study of this problem, since it records irrelevant aspects of behaviour. An experiment using apparatus which gives a continuous record of the force which a rat applies to a knob produces the following results. After much practice, pressing becomes sharp and brief and the amount of activity per reward is reduced. Under conditions of no (intentional) secondary reward the amount of activity during extinction is at first positively correlated with the average activity per reward during training, but the correlation diminishes as extinction proceeds. With auditory secondary reward there is no correlation.     

Partial reinforcement effects and type of reward

In two experiments 68 rats were trained to bar press or run down a straight runway for food or for water under conditions of either continuous reinforcement or partial reinforcement. In both experiments, there was greater persistence of behavior which had been reinforced with food than with water. In Expt 2, the partial reinforcement extinction effect (PREE) was observed with food reward, but not with water.Within the context of the experimental procedures used, it can be concluded that the rat has mechanisms for developing persistence which are dependent on the specific motivational system involved. This conclusion is related to theories of partial reinforcement effects and to possible biological origins of the mechanisms.     

A Mathematical Model of Depth Displacement with a Contracting Bar

When a vertical line segment contracts at both ends according to a (decelerating) time law of hyperbolic type, it appears to rotate around its midpoint. The phenomenon is quite surprising from the point of view of projective geometry as the segment should rather appear to recede along the sagittal plane. Apparent displacement in depth is however obtained when the bar simultaneously contracts and is displaced laterally on the frontal plane. But, here again, projective expectations are contradicted, because apparent displacement in depth occurs whether movement of the bar in two dimensions is hyperbolic (decelerating), uniform, harmonic (accelerating), or a mixture of the three. It is suggested here that the visual system operates in such a way as to minimize the differences between the lengths of the velocity vectors of all points of a moving configuration. The mathematical model derived from this hypothesis allows qualitative and quantitative predictions that are in good agreement with experimental results. Copyright 2001 Academic Press.     

Energetic and motor responses to increasing force requirements

The effects of increasing work (force) requirements on energy expenditure and response topography were examined in 7 rats pressing a beam to earn food. For the 1st 16 days, the force requirement was 5.52 x 10(-2) N (5.625 g). This increased by 4.91 x 10(-2) N (5 g) every 7th session until Ss had experienced 10 upward shifts. Following the 54.57 x 10(-2) N (55.625 g) condition, the original criterion was reinstated. During the augmented phase. Ss maintained stable reinforcement rates across conditions by increasing the peak force of beam pressing. These higher forces, occurring within 20 reinforcements of changing the force criterion, were produced primarily by increases in the rate of change of force (delta F/delta T). Also, while the rate of work performed on the beam increased, the overall energy expenditure fell. In contrast to these rapid adjustments, reinstating the original 5.52 x 10(-2) N (5.625 g) criterion resulted in only gradual alterations in motor performance.     

Seeing is believing? How reinterpreting perception as dynamic engagement alters the justificatory force of religious experience

William Alston’s Theory of Appearing has attracted considerable attention in recent years, both for its elegant interpretation of direct realism in light of the presentational character of perceptual experience and for its central role in his defense of the justificatory force of Christian mystical experiences. There are different ways to account for presentational character, however, and in this article we argue that a superior interpretation of direct realism can be given by a theory of perception as dynamic engagement. The conditions for dynamic engagement are such that there can be no absolute discontinuity between individual perceptual experiences and more public forms of inquiry, and this requirement has radical consequences for the prima facie justificatory force of religious experience.     

Changes in limb stiffness under conditions of mental stress

In 2 experiments, the effects of mental stress on limb stiffness were investigated. The relative contribution to arm stiffness of individual muscle activity, co-contraction, muscle reflexes, and postural adjustments were examined. In each experiment, participants (N = 24, Experiment 1; N = 16, Experiment 2) held their supinated hand under a tray that they were required to return to horizontal after it had been suddenly released. Electromyographic activity in the biceps and triceps muscles was recorded, as were elbow and wrist angles and tray displacement. In Experiment 1, mental arithmetic stress was shown to lead to decreased tray displacement (i.e., increased resistance) compared with displacements under the control, unstressed condition, as well as to increased elbow flexion before tray release. In Experiment 2, the increased resistance to perturbation caused by mental stress was found to be independent of initial elbow angle, but to vary as a function of the amount of upward force exerted before tray release. The authors conclude that stress-induced increases in limb stiffness result from changes in the initial position of the elbow, specified by its angle, together with the initial force exerted by participants to counteract the mechanical perturbations.     

An animal restraint for the study of high-resistance operants in the rat

An animal restraint system and response operandum suitable for the study of operant behavior in the rat is described. This system combined with an inexpensive Commodore microcomputer and Psychronix interface is well-suited for the study of response parameters. Rats voluntarily entered the restraint, showed no observable signs of excess stress, and were easily extricated at the end of the experimental session. A lever-pressing operant with an adjustable force requirement was readily shaped using automated procedures. Although this system was designed for the study of high-resistance operants, it has potential advantages for other operant applications, including studies of visual discrimination and experiments requiring restraint due to physiological recording.     

PROMPTING BAR PATRONS WITH SIGNS TO TAKE FREE CONDOMS

This study was designed to determine whether signs would prompt bar patrons to avail themselves of free condoms. The intervention at three “gay bars” involved placing a large sign directly above a container of free condoms; the sign gave statistics for the number of people who have died from AIDS in the state and pointed out that condoms can reduce the spread of AIDS. Additional signs placed in the restrooms gave information about safe sex practices and reminded patrons that free condoms could be obtained at a given location in the bar. An ABAB design was used, with a 2-week baseline, 2-week treatment with signs present, 2-week reversal with no signs, and 2-week reinstatement of treatment with signs present. For all three bars combined, 748 condoms were taken with signs present and 510 condoms were taken with signs absent. Overall, when signs were present, the number of condoms taken increased by 47%.     

Role of spatial and temporal coincidence in depth organization

The linking of spatial information is essential for coherent space perception. A study is reported of the contribution of temporal and spatial alignment for the linkage of spatial elements in terms of depth perception. Stereo half-images were generated on the left and right halves of a large-screen video monitor and viewed through a mirror stereoscope. The half-images portrayed a black vertically oriented bar with two brackets immediately flanking this bar and placed in crossed or uncrossed disparity relative to the bar. A pair of thin white 'bridging lines' could appear on the black bar, always at zero disparity. Brackets and bridging lines could be flickered either in phase or out of phase. Observers judged whether the brackets appeared in front of or behind the black bar, with disparity varied. Compared to conditions when the bridging lines were absent, depth judgments were markedly biased toward "in front" when bridging lines and brackets flashed in temporal phase; this bias was much reduced when the bridging lines and brackets flashed out of phase. This biasing effect also depended on spatial offset of lines and brackets. However, perception was uninfluenced by the lateral separation between object and brackets.     

Transfer of effort across behaviors

A series of experiments investigated the effects of required force and number of responses per reinforcer upon the subsequent performance of a second behavior. In the first experiment, a group of rats required to complete five round trips in an alley per food pellet subsequently bar-pressed for food at a greater rate than a group rewarded for each round trip or a control group that did not receive the alley experience. In the second experiment, a group required to apply a 70-g bar-press force subsequently shuttled for food at a greater rate than a group required merely to touch the lever or a control group that did not undergo the lever-press manipulation. The third experiment found that the force effect persisted across all five test sessions and was attributable to differences both in response speed and interresponse time. The fourth experiment found that both the necessary bar-press force and number of bar presses per reward affected subsequent shuttling in extinction. Two alternative interpretations of these results were compared: (a) the degree of accustomed effort per reinforcer becomes a generalized component of instrumental behavior or (b) high effort increases the habituation frustration-produced disruptive responses.