In an experiment on conditioned suppression of licking in thirsty rats, subjects received either one or two trials to a tone-light compound, either preceded or not preceded by four conditioning trials to the light alone. Prior conditioning to the light blocked conditioning to the tone in subjects receiving two compound trials but not in those receiving only one compound trial. The blocking observed in the two-trial groups was abolished either by the addition of an unexpected second posttrial shock 10 sec after the first on each compound trial or by the omission of an expected second, posttrial shock. The comparable operations had no effect on conditioning to the tone in the one-trial group. In this preparation, both blocking and the attenuation of blocking by surprising changes in reinforcement appear to require more than one trial to appear.In experiments on conditioned suppression in rats, Kamin (1969) established that prior conditioning to one component of a compound conditioned stimulus (CS) could prevent or block conditioning to the other component and that this blocking effect was abolished, or at least attenuated, if a surprising change in reinforcement was programmed to occur on compound trials. In Kamin's original experiments, the change in reinforcement consisted of either an increase in intensity of the shock reinforcer or the addition of an unexpected second, posttrial shock shortly after the first shock reinforcer on each compound trial. A possible interpretation of Kamin's results, therefore, is that blocking occurs because prior conditioning ensures that there is little or no discrepancy between the reinforcement that occurs on compound trials and the reinforcement already expected by the subject on the basis of the pretrained component (Rescorla & Wagner, 1972). Successful excitatory conditioning to the added component requires such a positive discrepancy between obtained and expected reinforcement, which is provided by an increase in shock intensity or the addition of a second shock.

No abstract

Five experiments, all employing conditioned suppression in rats, studied inhibitory conditioning to a stimulus signalling a reduction in shock intensity. Experimental subjects were conditioned to a tone signalling a 1.0 mA shock and to a tone-light compound signalling a 0.4 mA shock. On a summation test in which it alleviated the suppression maintained by a third stimulus also associated with the 1-0 mA shock, the light was established as a conditioned inhibitor. Retardation tests gave ambiguous results : the light was relatively slow to condition when paired, either alone or in conjunction with another stimulus, with the 0.4 mA shock, but the difference from a novel stimulus control group was not significant. Two final experiments found no evidence at all of inhibition on a summation test in which the light was presented in conjunction with a stimulus that had itself been associated with the 0.4 mA shock. The results of these experiments have implications for the question of what animals learn during the course of inhibitory conditioning.

The paper by Cotton and Evans presents a useful review of research on the Men lens procedure. However, as the Yranchised Men lens practitioner" referred to in the paper, I am concerned that its value as an investigation of the effects of lenses is limited by a number of factors. Unfortunately, analysis of the results is restricted by the fact that it has not been possible to access the raw data.However, based on the data contained in the paper and in the thesis (Evans, 1988) from which the research component of it emanates, the following observations can be made. Conditions of Testing Development of Effect3It is important to appreciate the true nature of the study, which evaluated the immediute ef€ects of Irlen lenses. The assumption is made in the Cotton and Rquests for reprints should be sent to G. L. Robinson,

Porous materials are of great interest because of improved energy absorption over their solid counterparts. Their properties, however, have been difficult to optimize. Additive manufacturing has emerged as a potential technique to closely define the structure and properties of porous components, i.e. density, strut width and pore size; however, the behaviour of these materials at very high impact energies remains largely unexplored. We describe an initial study of the dynamic compression response of lattice materials fabricated through additive manufacturing. Lattices consisting of an array of intersecting stainless steel rods were fabricated into discs using selective laser melting. The resulting discs were impacted against solid stainless steel targets at velocities ranging from 300 to 700 m s −1 using a gas gun. Continuum CTH simulations were performed to identify key features in the measured wave profiles, while 3D simulations, in which the individual cells were modelled, revealed details of microscale deformation during collapse of the lattice structure. The validated computer models have been used to provide an understanding of the deformation processes in the cellular samples. The study supports the optimization of cellular structures for application as energy absorbers.