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London’s population and hospitals: 1801–1971
Published in Leslie Mayhew, Urban Hospital Location, 2018
To recap briefly, the basis for the analysis was provided by central place theory, which was originally developed by Christaller to explain the spatial arrangement of cities, towns, villages and other settlements in a region. To apply this theory to hospital systems within cities, therefore, certain changes had to be made to the basis of the theory. Besides a reduction in the geographic scale of enquiry, these changes included new assumptions about the objectives of a central place system; the introduction of different forms of demand behaviour; alternatives to the standard, regular hexagonal set of market areas; different measures of accessibility costs; and some very simple dynamics to deal with the internal changes in the size and distribution of population in city regions.
Pitch and timbre
Published in Stanley A. Gelfand, Hearing, 2017
Traditional place theory (Chapter 4) would suggest that the missing fundamental is due to energy present at the fundamental frequency as a result of auditory distortions. In other words, the difference tone f2 − f1 would be the same as the missing fundamental since, for example, 1100 − 1000 = 100 Hz. However, this supposition cannot be true for several reasons. First, the missing fundamental differs from combination tones in several dramatic ways. For example, the missing fundamental is audible at sound pressure levels as low as about 20 dB (Thurlow and Small, 1955; Small and Campbell, 1961), but difference tones are not heard until the primary tones are presented at 60 dB SPL or more (Bekesy, 1960; Plomp, 1965). Second, aural beats can be heard if a probe tone is presented to a subject's ear at a frequency close to that of a difference tone (which is actually represented at a place along the basilar membrane), but beats do not occur when the probe is added to the missing fundamental (Schouten, 1940). Third, whereas stimulus and difference tones (which have a presence in the excitation pattern of the basilar membrane) can be masked, the missing fundamental cannot be masked. And fourth, the missing fundamental can be produced by stimulus harmonics that cannot interact in the cochlea because they have been presented one after the other or separately to the two ears.
ENTRIES A–Z
Published in Philip Winn, Dictionary of Biological Psychology, 2003
The foregoing processes have the consequence that the location of vibration along the length of the basilar membrane, and thus the identity of the subset of hair cells and afferent nerves activated, depends on the frequency content of the acoustic stimulus. This is known as the PLACE THEORY. The cochlea can be conceptualized as a linear array of frequency-tuned channels, each functioning relatively independently. The task of any one of these channels is to encode information about the presence, timing and amplitude of stimulus energy at its preferred frequency, and to transmit that information to the brain. For frequencies less than about 3000 Hz, the inner hair cell receptor potential has DEPOLARIZATION and HYPERPOLARIZATION half-periods that are phase-locked to upward and downward motions of the basilar membrane, respectively. Since neurotransmitter release is coupled to hair cell depolarizations, this has the consequence that cochlear nerve fibres are excited by unidirectional elevations of the basilar membrane. Restated, this means that for low frequency sounds, cochlear nerve cells generate a typical ACTION POTENTIAL that is time-locked to oscillations of the basilar membrane at the innervated site and thus to the phase of the stimulus. This constitutes a temporal code for frequency, since the time between spikes will be equal to the stimulus period, or an integral multiple of it. Either by sampling the SPIKE activity of a single such nerve for some duration, or by sampling a number of such nerve cells concurrently, the brain is able to determine the low-frequency spectral content of the sound. This is known as the volley principle.
Art and knowing in health management education
Published in Medical Teacher, 2022
A/r/tography is a research methodology that entangles and performs what Gilles Deleuze and Felix Guattari (1987) refer to as a rhizome. A rhizome is an assemblage that moves and flows in dynamic momentum. The rhizome operates by variation, perverse mutation, and flows of intensities that penetrate meaning, opening it to what Jacques Derrida (1978) calls the ‘as yet unnameable which begins to proclaim itself’ (p. 293). It is an interstitial space, open and vulnerable where meanings and understandings are interrogated and ruptured. Building on the concept of the rhizome, a/r/tography radically transforms the idea of theory as an abstract system distinct and separate from practice. In its place, theory is continuously in a state of reconstruction and becoming something else altogether (Irwin and Springgay 2008, p. xx).
Spatial hearing processing: electrophysiological documentation at subcortical and cortical levels
Published in International Journal of Neuroscience, 2019
Nematollah Rouhbakhsh, John Mahdi, Jacob Hwo, Baran Nobel, Fati Mousave
AEP’s investigation into spatial lateralization and localization of sounds has dedicated on individual ILDs and ITDs without taking into account a real acoustic environment [33–35]. In a study to investigate the effect of locating sound sources on the auditory evoked response, Butler [34] found a significant increase in amplitude (N1P2) when sound staggered between two loudspeakers in azimuth (at either 270° and 315°, 270° and 0°, or 270° and 90°) or in elevation (at 45° above and 45° below ear level) planes. He attributed these findings to a cortical organization of place theory for perception of auditory space. Smith, Hsieh [36] and Wambacq, Koehnke [35] found a significant amount of AEP activation in both children and adults in an ILD condition of 20 dB compared to an ILD-absent condition. This experiment showed a negative activation in adults at 100 ms, a positive prolonged wave in children at 250 ms and a positive wave in both populations at 200 ms.