Biomedical subjects
Nicholas J Wade
Publications and source records attributed to Nicholas J Wade.
The legacy of phantom limbs.
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The Chimenti controversy.
Jacopo Chimenti (c 1551-1640), an artist from Empoli, made two sketches of a young man holding a compass and a plumb line. When these were seen, mounted next to one another, by Alexander Crum Brown in 1859, he combined them by overconvergence and described the stereoscopic depth he saw. Brown's informal observation was conveyed to David Brewster, who suggested that the drawings were produced for a stereoscope, possibly made by Giovanni Battista della Porta. There followed a bitter debate about the supposed stereoscopic effects that could be seen when the pictures combined. Brewster's claims were finally dispelled when precise measurements were made of the drawings: some parts were stereoscopic and others were pseudoscopic. Brewster's attempts to wrest the invention of the stereoscope from Wheatstone were unsuccessful.
On nystagmus, saccades, and fixations.
Investigations of the ways in which the eyes move came to prominence in the 19th century, but techniques for measuring them more precisely emerged in the 20th century. When scanning a scene or text the eyes engage in periods of relative stability (fixations) interspersed with ballistic rotations (saccades). The saccade-and-fixate strategy, associated with voluntary eye movements, was first uncovered in the context of involuntary eye movements following body rotation. This pattern of eye movements is now referred to as nystagmus, and involves periods of slow eye movements, during which objects are visible, and rapid returns, when they are not; it is based on a vestibular reflex which attempts to achieve image stabilisation. Post-rotational nystagmus was reported in the late 18th century (by Wells), with afterimages used as a means of retinal stabilisation to distinguish between movement of the eyes and of the environment. Nystagmus was linked to vestibular stimulation in the 19th century, and Mach, Breuer, and Crum Brown all described its fast and slow phases. Wells and Breuer proposed that there was no visual awareness during the ballistic phase (saccadic suppression). The saccade-and-fixate strategy highlighted by studies of nystagmus was shown to apply to tasks like reading by Dodge, who used more sophisticated photographic techniques to examine oculomotor kinematics. The relationship between eye movements and perception, following earlier intuitions by Wells and Breuer, was explored by Dodge, and has been of fundamental importance in the direction of vision research over the last century.
Dodge-ing the issue: Dodge, Javal, Hering, and the measurement of saccades in eye-movement research.
Dodge, in 1916, suggested that the French term 'saccade' should be used for describing the rapid movements of the eyes that occur while reading. Previously he had referred to these as type I movements. Javal had used the term 'saccade' in 1879, when describing experiments conducted in his laboratory by Lamare. Accordingly, Javal has been rightly credited with assigning the term to rapid eye movements. In English these rapid rotations had been called jerks, and they had been observed and measured before Lamare's studies of reading. Rapid sweeps of the eyes occur as one phase of nystagmus; they were observed by Wells in 1792 who used an afterimage technique, and they were illustrated by Crum Brown in 1878. Afterimages were used in nineteenth-century research on eye movements and eye position; they were also employed by Hering in 1879, to ascertain how the eyes moved during reading. In the previous year, Javal had employed afterimages in his investigations of reading, but this was to demonstrate that the eyes moved horizontally rather than vertically. Hering's and Lamare's auditory method established the discontinuous nature of eye movements during reading, and the photographic methods introduced by Dodge and others in the early twentieth century enabled their characteristics to be determined with greater accuracy.
The search for a sixth sense: the cases for vestibular, muscle, and temperature senses.
The five senses of sight, hearing, smell, taste, and touch, enumerated by Aristotle, were incremented in the early-nineteenth century by the muscle sense, multiple dimensions of touch, and a movement sense. Aristotle explicitly excluded a sixth sense, and five remains the number of senses in popular imagination. The division of touch into several sensations was entertained and rejected by Aristotle, but it was given anatomical, physiological and psychophysical support in the late-nineteenth century. A separate muscle sense was proposed in the late-eighteenth century, with experimental evidence to support it. However, before these developments, behavioral evidence of the vestibular (movement) sense was available from studies of vertigo, although it was not integrated with the anatomy and physiology of the labyrinth until the nineteenth century. The history of the search for a sixth sense is outlined, and the evidence adduced to support the divisions is assessed. Behavioral evidence generally has been accorded less weight than that from anatomy and physiology.
William Porterfield (ca. 1696-1771) and his phantom limb: an overlooked first self-report by a man of medicine.
EARLY REPORTS OF phantom limbs by Ambroise Paré and René Descartes were based on second- or third-hand descriptions provided by amputees. William Porterfield (ca. 1696-1771) was a prominent Scottish physician and was possibly the first man of medicine to write about his experiences after having a leg amputated. Porterfield was an authority on vision; he devised the first optometer and examined accommodation after cataract operations. Rather than using the phenomenon of a phantom limb to question the veracity of the senses (as Descartes had done), Porterfield integrated his phantom limb experiences into his general account of sensory function.
Monocular alignment in different depth planes.
We examined (a) whether vertical lines at different physical horizontal positions in the same eye can appear to be aligned, and (b), if so, whether the difference between the horizontal positions of the aligned vertical lines can vary with the perceived depth between them. In two experiments, each of two vertical monocular lines was presented (in its respective rectangular area) in one field of a random-dot stereopair with binocular disparity. In Experiment 1, 15 observers were asked to align a line in an upper area with a line in a lower area. The results indicated that when the lines appeared aligned, their horizontal physical positions could differ and the direction of the difference coincided with the type of disparity of the rectangular areas; this is not consistent with the law of the visual direction of monocular stimuli. In Experiment 2, 11 observers were asked to report relative depth between the two lines and to align them. The results indicated that the difference of the horizontal position did not covary with their perceived relative depth, suggesting that the visual direction and perceived depth of the monocular line are mediated via different mechanisms.
The pursuit of Leonardo's constraint.
Leonardo da Vinci (1452-1519) identified two stimulus situations that cannot be painted faithfully on a canvas: (a) when two objects are located in the same direction with respect to the painter's head, and (b) when parts of a surface are visible to one eye, but occluded from the other eye. He analysed these situations in terms of rays being emitted from the two eyes and, aside from the origin of the rays, the projective geometry he used was correct. His analyses showed that what can be seen from two vantage points cannot be represented on a canvas, because a 'correct' painting must be created from a single 'station point'. He was struck by the consequence of this fact that the depth seen on a canvas cannot match that of viewing the scene with two eyes. Subsequent visual scientists focused on Leonardo's observation about the lack of vivid depth in a picture. We argue that a complete understanding of what we see in the two stimulus situations requires consideration of visual direction in addition to visual depth. More specifically, we argue that the visual directions of the two objects, (a) above, and the visual direction of the monocular areas, (b) above, are dependent upon the constraint that two opaque objects cannot be represented in the same direction. Demonstrations that readers can perform, and that support this argument, are provided on the Perception website at http://www.perceptionweb.com/perc0102/ono.html.
Charles Wheatstone (1802-1875).
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Perceptual pilgrimages.
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The neuroscience of Helmholtz and the theories of Johannes Müller. Part 1: Nerve cell structure, vitalism, and the nerve impulse.
Hermann Helmholtz made monumental contributions to the neural sciences in the second half of the nineteenth century. Among his earliest achievements were experiments that challenged vitalism, microscopic studies on the structure of the nerve cell and its processes, and the first reasonable estimates of the speed of nerve transmission based on physiological experiments. In this, the first of a two-part article, we review Helmholtz's early contributions in biographical context and with reference to Johannes Müller's own thoughts. We reveal how Johannes Müller, considered by many to be the greatest physiologist of the first half of the nineteenth century, helped to launch and shape Helmholtz's career. We also show that Helmholtz was only willing to accept some of his mentor's theories, even though he had great admiration for Müller. The point will be made that Helmholtz owed a great debt to Müller, but even from his student days in Berlin he was an independent thinker with his own agenda, and never his strict disciple.
The neuroscience of Helmholtz and the theories of Johannes Müller. Part 2: Sensation and perception.
In this, our continuation paper on Helmholtz and Müller, we examine Helmholtz's contributions to sensation and perception, with emphasis on his extension and modification of Müller's theory of specific nerve energies. The material is again presented in biographical-chronological context. We also examine Helmholtz's views on depth and space perception, and his empirical theory of knowledge, which are also compared to Müller's views. It will be shown that Helmholtz remained stimulated by the thoughts and doctrines of Johannes Müller in the sensory-perceptual part of his career, which began early in the 1850s and ended with his death. Nevertheless, Helmholtz's own experiments and new discoveries by others sometimes led him to quite different conclusions.