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Sensory System
Published in Peter Kam, Ian Power, Michael J. Cousins, Philip J. Siddal, Principles of Physiology for the Anaesthetist, 2020
Peter Kam, Ian Power, Michael J. Cousins, Philip J. Siddal
The sensory system can code the intensity, location and quality of a stimulus. The modality of sensation depends on the specificity of the receptor and the location of a stimulus related to the receptive field. Regions of the body that are densely innervated (lips and fingers) can provide precise information about the shape, size and position of the stimulus. A large or suprathreshold stimulus can also increase the number of neurons responding by the recruitment of more sensory units. Stimulus intensity may be coded by the frequency of impulse in each sensory unit or by the number of active sensory units. There appears to be a linear relationship between the receptor generator potential amplitude and the sensory nerve action potential frequency. The stimulus intensity may have a linear or a logarithmic (Weber–Fechner law) relationship with the frequency of action potentials in the sensory nerves.
Methods in Physical Science: Feelings Don’t Matter
Published in David E. H. Jones, Why Are We Conscious?, 2017
Our senses were later scrutinized scientifically by Gustav Fechner. He wrote in 1860 that the smallest noticeable sensory difference is about 1 to 2 percent. Thus one might expect that sort of difference between different observers. This measurement is now part of sensory psychology as the Weber-Fechner law. In chemistry, it often crops up in consistent differences between analysts. Such differences probably arise from a set of consistent habits built up by each individual analyst, perhaps some personal way of making a filtration or of reading a burette. Hence the value of ‘standard samples’, which should give the same analysis even if analysed by different workers or at different times. This is a good example of the various tricks which experimentalists have evolved to overcome the problems which may arise where human observations differ worryingly. Another is the universal reliance on scientific instruments. We all have different ideas of the temperature, but the reading on a thermometer can be seen and agreed upon by everybody. We are each sensitive to electricity in our own way, but again, the reading on a voltmeter is objective. We may even differ about what we see, but a photograph can be shared by all observers. It is our good fortune that many essentially sporadic and unpredictable events, like those around cosmic rays, happen often enough for single experimental scientists to be able to study them when they occur. As a result, many of their individual reports may be built up into a useful understanding.
MRCPsych Paper A1 Mock Examination 3: Questions
Published in Melvyn WB Zhang, Cyrus SH Ho, Roger Ho, Ian H Treasaden, Basant K Puri, Get Through, 2016
Melvyn WB Zhang, Cyrus SH Ho, Roger CM Ho, Ian H Treasaden, Basant K Puri
A 50-year-old woman has received six sessions of electroconvulsive therapy (ECT). She complains of significant recent memory loss while remote memories remain intact. This phenomenon is known as Gestalt’s lawMarr’s lawRibot’s lawTarasoff’s lawWeber–Fechner law
Performance of a new device for the clinical determination of light discomfort
Published in Expert Review of Medical Devices, 2020
Robert Montés-Micó, Alejandro Cerviño, Noelia Martínez-Albert, José V. García-Marqués, Sarah Marie
According to this setup, the discomfort glare quantified by the system would be the ‘saturation’ or ‘absolute’ glare, as per Pierson description [10] previously mentioned, also agreeing with the description by Mainster and Turner [12]. In order for the user not to face intolerable glare, ascendant method is used. Light increase is automatic, as manual adjustments may induce bias in the measurement and reduce reliability in between-subjects comparison. Moreover, when light reaches the second discomfort threshold (RD) or the maximum intensity of the tool, the light automatically turns off. Vertical illuminance at eye level that produced discomfort thresholds is provided in Lux. According to the Weber-Fechner law, the intensity of a sensation is proportional to the logarithm of the intensity of the stimulus causing it, thus the choice for the increments in percentage of intensity [53]. Two methods of light increase are used (both described in the literature, see epigraph 2.5). For continuous increase, light starts at 25 Lux for 5 seconds and increases every second using a 20% increase step. The continuous ramp contains 34 steps and maximum time duration is 38 seconds. This progressive increase (also used by Adams et al. [15]) allows the visual system to adapt a little. The second method is flashing increase. The light starts at 10 Lux for 5 seconds before increases instantaneously to 25 Lux for half a second and goes back to 10 Lux for 2 seconds before the next stimuli. Increase between each step is 44% in order to have similarity in light levels prevented in the method of light increase without a too-long duration of the flashing ramp. The flashing ramp includes 17 levels and a maximum duration of 43 seconds (to reach 8509 Lux). This flashing increase (also used by Vanagaite et al. [14]) does not provide enough time for the visual system to adapt. These two methods have been selected in order to reflect the most bothering situations in everyday life.