In Integrative Action, Sherrington introduced his cinematographic studies as pertaining to the question of whether or not it was possible to extend his conclusions regarding nervous activity in the simple reflexes to the analysis of sensations. For the majority of the book, he had, as he noted, supposed the animal 'a puppet without passions, memory, feelings, sensations, let alone ideas concrete or abstract.' Now, in his final chapter, he queried whether 'we [can] at all compare with the simultaneous co-ordination of the nervous factors in a motor reflex the synthesis of the nervous elements whose combination underlies a simple sense-perception?' Though he notably did not go so far as to make any positive claim, he thereby intimated that complex psychological phenomena might be explained by reference to his physical interpretation of nervous action. Less clear from Sherrington's text, however, is that were such a claim to have been established, it would have turned back a tide of opinion that had been gaining ground in physiology since at least the middle of the nineteenth century.

That McDougall had arrived at his conclusions following a close engagement with German physiological psychological research practices was no coincidence. By the middle decades of the nineteenth century, an intimate relation had emerged in Germany between the study of the senses through the generation of illusion, and debates surrounding physical and vital explanations of physiological function. Most prominently, Hermann von Helmholtz had argued that the perception of nature was dependent in the final analysis on an act of judgement that could not be understood in terms of bodily activities in any meaningful way. The living body, as the Helmholtz of the 1860’s conceived it, was a physical structure the behaviour of which could be characterized in terms of mathematical laws. As such, it constituted a medium through which impulses from the external world were conveyed to the mind. Whilst nerves were conveyors of sensory stimulations, it was the function of a physiologically-inaccessible mind to arrive at judgements regarding nature. Mind and sense organs thereby formed two elements of a perceptual system that retained a distinct separation between the immediate physiological conditions of sensation and their (physiologically-undetermined) reception. However, Helmholtz’s sensory model had not gone unopposed. Starting in 1863, Hering had embarked on a lengthy campaign against any separate consideration of sensations and sense-organs themselves. Hering and his supporters drew on a longer-established tradition of psycho-physiological research to develop a sophisticated set of demonstrations and arguments identifying visual illusions not with the inaccurate judgements of a physiologically-independent mind, but with the physiological make-up of the organs of sense. As already noted, Hering came to characterize sensation as the product of autonomously-acting organic forces that had only oblique relation to any bodily-independent judgement.

One of the principal means by which Helmholtz, Hering and their various supporters and detractors conducted their disputes was via the creation and demonstration of a vast array of illusion-generating devices and mechanisms. Müller's Göttingen laboratory had been well stocked with equipment developed for the illusory study of colour vision, and Münsterberg had acquired a wide range of devices for sensory and particularly visual experimentation at Freiburg. In acquiring Münsterberg's psychological laboratory, Sully had thereby helped bring a set of research questions to Britain that had hitherto generally only appeared in the country in terms of broader enquiries concerning the relation of matter to spirit (for example in the study of Mesmerism), or, as frequently, optics. The tools that Münsterberg's laboratory contained invited investigation of sensory and more generally psychological problems within a very different setting than these latter sciences.

The relevance of these developments to Sherrington's cinematographic studies are brought out in his initial foray into the study of visual sensations, published in 1897. This suggested a direct parallel between two phenomena that had been current amongst philosophers of optics since the 1830s. These were studies relating on the one hand to the shortest time that an eye could be exposed to a flash of light and an associated light-sensation be experienced, and on the other to the production of a sense of continuous experience via repeated exposure to radically different visual stimuli. Regarding the first of these, nineteenth-century natural philosophers had been fascinated by a wide range of phenomena that occurred over very short intervals of time. The nature of sparks, bubbles and vibrations were interrogated via tools designed for the 'fixing' of transient phenomena, of which the photographic plate was only one: these devices drew attention to a range of previously scientifically elusive phenomena. Within the German context especially, a set of physiological problems associated with these phenomena emerged that considered the processes by which stimulation of the eye actually resulted in visual experience. One particularly prominent theme was the fact, embodied by the motion-sensation-generating phenakistoscope (and later Muybridge's zoopraxiscope), that a series of short stimulations could, through the phenomena of 'persistance of vision', create an illusion of temporal continuity. In 1885, Marey's associate Adolph-Moïse Bloch adapted a version of the intermittently-obscured lamps that William Henry Fox Talbot and Simon von Stampfer had developed during the 1830s to physiological investigation. Where Talbot sought to measure light intensity itself, Bloch hoped to establish a law regarding the rates at which individual sensation-flashes produced a continuous light-sensation under different conditions. Such studies prompted a range of physiological investigations into Stampfer's 'stroboscopic' effects during the 1890s. Sherrington's 1897 study however dealt primarily with a parallel set of investigations into the 'fusion' not of light-, but of colour-sensations. Again drawing on the optical studies of the 1830s, the physicist Ogden Rood had in 1893 presented what he considered method by which colours might be differentiated according to their 'reflecting power.' Spinning a circular disc on which alternating bands of light and shade had been painted, Rood measured the rate of rotation required to eliminate the sense of intermingling or 'flicker' between them. Exposing observers to intermittently contrasting stimuli created sensory effects not present when equipment was at rest. Questions of sensation were increasingly coming to be addressed not in terms of spatial differentiation (as in McDougall's studies), but rather in relation to questions regarding temporal continuity. The phenomena studied by Sherrington - the physiological conditions pertaining to the production of light- and colour-sensation - thus came together (or rather were re-connected) via a set of experiments that had been foundational for the emergence of laboratory cinematography.

Nor was Sherrington the only British physiologist to experiment with illusions of temporal continuity at this time. Shortly after Sherrington's initial flicker study came out, a paper by his Cambridge compatriot Otto Fritz Frankeau Grünbaum was published in the Journal of Physiology. This study, which also addressed the rate at which alternating stimuli fused into continuous perception, strove for far greater precision than had Sherrington. Rather than direct both eyes to an external stimulus in the shape of a rotating disc, Grünbaum created a mechanism (fig. 3) that could project two separate beams of light onto the retina of a single eye. One of these beams was constant, thus constituting a point of comparison. The other beam however was interrupted by a rotating disc with angular segments cut out of it. By rotating this disc at different speeds, Grünbaum sought to arrive at a more accurate estimation of the rates of exposure necessary for the experiences of different brightnesses. The parallels between the establishment of illusion-generating devices within physiology laboratories and that of cinematographic technology more generally are prominent here. One of the key elements of the cinematograph - and one of the most difficult pieces to co-ordinate with the movement of celluloid film-strips - was a disc or 'shutter' (similar to the ones Talbot and von Stampfer had developed) that cut off the projection of light at intervals proportional to the replacement of images on the projector. The minimal rate at which cinematographic images had to be replaced and exposed to view was determined by the rate at which images could be perceived as individual, rather than a continuous moving picture - i.e. by the phenomena of persistence of vision. During the 1890s, the physiological study of flicker fusion and the construction of cinematographic devices went hand in hand.

By 1902, Sherrington had begun to develop a device that surpassed even Grünbaum's in experimental precision. Crucially, in addition to constituting a means by which the temporal phenomenon of visual flicker could be studied, this experiment also incorporated a spatial element. Sherrington's device (fig. 4) placed an incandescent lamp (such as might be used used in a projecting device) in the middle of a rotating cylindrical screen, into which three rows of rectangular windows had been cut. Surrounding this cylinder was a casing, with a further four small holes cut in a step formation on its side. As the inner cylinder turned, thin beams of light were intermittently projected at intervals through these holes. Just as in Grünbaum's study, the rate at which light was projected could be varied and the rotation rates at which 'flicker fusion' appeared and disappeared ascertained. But Sherrington sought even greater accuracy than had Grünbaum. By making the holes through which light passed very small, confined the optical effects produced to as few nerves as possible. Moreover, by positioning the experimental subject at a carefully calculated distance from the lamp, and providing them with correcting lenses, the holes on each side would project light onto an optically 'equivalent' point on each retina. Whereas Grünbaum's device had exposed different half of one retina to different rates of stimulation, Sherrington's could (by varying the size of the rectangles cut into the cylindrical screen) expose 'corresponding' points on each to the same. McDougall's concerns regarding the alternation of spatial experience as attention wavered between the eyes were thereby put in contact with studies of temporal continuity via rapidly successive stimulatory effects.

Sherrington brought all of the resources that Daston and Galison associate with mechanical objectivity to bear in conducting his cinematographic experiment. Observers were provided with an electronic key that, when pressed, would mark a myograph cylinder, on which the rate of rotation of the screen at that point was recorded. Even more strikingly, he went to great lengths to ensure than observers remained as passive as possible to the phenomena that they experienced. Seated in a 'dark compartment' screened off from the experimental set-up allowed a subject to 'give his sole attention to the watching of the illuminated discs.' Once the beams of light had been corrected by the lenses, the interruption of further light sources was prevented by the introduction of 'artificial pupils' between the lenses and the eye. The propensity of some observers to move their head when they closed one or another eyelid was eliminated by the utilization of 'blackened aluminium side-flaps' that could be secured in place as needed. Finally, 'fixation of the observer's head was secured by a solidly made wooden rest, supporting adjustable chin and forehead pieces.' The passivity of subjects to the stimulating mechanism was thereby, it seemed, ensured.

Sherrington's studies sought to bring the production of cinematographic effects of continuity within the purview of his physical physiological schema. His goal was not merely to arrive at an accurate estimation of the rate at which flickering sensations transformed into continuous ones, but also to interrogate the relationship between the retina, the nerves, and visual sensations more generally. Hering's studies had suggested that the optic nerves had to connect before they arrived at the centre of consciousness, as it was in the eyes and their associated nerves that vision was produced. Helmholtz's insistence that knowledge was a judgemental construct, in contrast, seemed to imply that all sensory organs were connected with the cerebrum individually - it was only through the mind bringing individual sense-experiences together than external perception was generated. By creating a situation in which 'corresponding' points on the retina could be stimulated in similar but crucially alterable ways, Sherrington sought to establish with greater surety than had McDougall the modes of interaction between visual fields. By blocking off some of the holes and one or another of the rectangles cut into the rotating screen, it was possible to create situations in which retinal points could be stimulated either simultaneously or alternately, but always at the same rate. Thus, Sherrington hoped, it would be possible to examine whether stimulatory effects were 'additive' between corresponding nerves, or whether McDougall's contentions regarding their 'mutual inhibition' were in fact accurate. If binocular visual sensation could be shown to be additive, Helmholtz's conclusions could be confirmed. If they inhibited one another, Hering would be supported. Here then appeared a crucial test of a long-standing dispute within physiological psychology.

Despite the lengths to which Sherrington went to ensure that both his subjects and his objects were as carefully arranged and closely controlled as possible, however, he was unable to reach any firm conclusions regarding his results. Sherrington's aim had been to evaluate the extent to which his conclusions regarding the physical nature of simple reflex action could be brought to bear on the interpretation of complex sensory phenomena. But when it came to drawing conclusions from these studies, he himself wavered between the two above-noted possibilities. The problem was not - as had hampered so many prior studies in this vein - disagreement amongst individual observers. Rather, it concerned the seemingly contradictory nature of the results themselves. Whether retinal stimulations could be said to sum together or mutually interfere depended, it seemed, on the mode of stimulation: ''corresponding retino-cerebral' points', he perplexedly concluded, 'retain individuality as regards time-relations... [but are] completely confluent by reference to visual space.' Furthermore the 'rule of combination' revealed by the experiment 'finds little solution by appeal to summation or interference of retinal and purely physiological processes.' Though Sherrington leant towards a Helmholtzian conception of visual sensation, introspective sensory investigation, when conducted under carefully controlled laboratory conditions, did not lead to clear-cut physiological conclusions.

The possibility that the study of visual illusions could inform study of the extent to which optic nerves actively contributed to sensation had taken Sherrington a long way from his starting point of the physical interaction of individual nerves. Integrative Action continued to portray the study of 'sensual reaction' as at least potentially part and parcel of that of nerve reactions more generally. Although the difficulty of interpreting the flicker experiment showed that 'hasty conclusions' regarding the parallels between simple and 'sensual' reflexes were unwise, it was nevertheless possible to insist on a 'likeness of nervous reactions expressed by muscular and other effector-organs to reactions whose evidence is sensual.' More generally, the correspondence of sensations to positions in space, to which the body could direct its actions, indicated that 'physiology and psychology, instead of prosecuting their studies... more strictly apart... will find it serviceable for each to give the results achieved by the other even closer heed than has been customary hitherto.' Nevertheless, Sherrington's cinematographic studies were not a success in his own physiological terms, and he would not produce any further work in this vein. By the end of the First World War, the rooms at Oxford that McDougall used for his psychological experimentation had been requisitioned for more strictly physical physiological investigation. Such differentiation of physiological from psychological endeavour would set a trend for these sciences during the first half of the twentieth century.