9.1 Introduction Psychophysics is the oldest field of the science of psychology. It stems from attempts in the nineteenth century to measure and quantify sensation. It attempts to quantify the relationship between a stimulus and the sensation it evokes, usually for the purpose of understanding the process of perception. Historically, psychophysics has centred around three general approaches. The first involves measuring the smallest value of some stimulus that a listener can detect – a measure of sensitivit
7.2 Coding of information in the higher auditory centres We have seen that in the cochlear nerve, information about sound intensity is coded for in two ways: the firing rates of neurons and the number of neurons active. These two mechanisms of coding signal intensity are found throughout the auditory pathway and are believed to be the neural correlates of perceived loudness. The tonotopic organisation of the auditory nerve is also preserved throughout the auditory pathway; there are tonotopic maps within each of the auditory nerve relay nuclei, the
3.5.2 Mechanical force directly opens and closes transduction channels It is believed that tip links aid in causing ‘channels’ to open and close near the top of the hair cell (Figure 16). Tip links are filamentous connections between two stereocilia. Each tip link is a fine fibre obliquely joining the distal end of one stereocilium to the side of the longest adjacent process. It is thought that each l
3.2 The anatomy of the cochlea The cochlea has a spiral shape resembling the shell of a snail (Figure 4a). You can approximate the structure of the cochlea by wrapping a drinking straw 2.5 times around the tip of a sharpened pencil. The hollow tube, represented by the straw, has walls made of bone and the central pillar of the cochlea, represented by the pencil, is a conical
3.1 Introduction The inner ear (Figure 3) can be divided into three parts: the semicircular canals, the vestibule and the cochlea, all of which are located in the temporal bone. The semicircular canals and the vestibule affect the sense of balance and are not concerned with hearing. However, the cochlea, and what goes on inside it, provides
1 Sound reception: the ear In order to hear a sound, the auditory system must accomplish three basic tasks. First it must deliver the acoustic stimulus to the receptors; second, it must transduce the stimulus from pressure changes into electrical signals; and third, it must process these electrical signals so that they can efficiently indicate the qualities of the sound source such as pitch, loudness and location. How the auditory system accomplishes these tasks is the subject of much of the rest of this block. We will
2.5.1 Quantum mechanics and chance The real quantum revolution dates from the formulation of quantum mechanics by Werner Heisenberg (1901–1976) and others in 1925, and its physical interpretation by Max Born (1882–1970) in 1926. However, before attempting even the most basic sketch of quantum mechanics let's take a small diversion into the realm of philosophy. The basic working philosophy of most scientists, including those who say they have no philosophy, is a kind of realism. (Philosophers recognise m
2.3.2 Equilibrium and irreversibility As the science of thermodynamics developed beyond its industrial roots, two powerful ideas came to the fore – equilibrium
and irreversibility. These ideas were already implicit in studies of heat. You have already seen that heat flow from a hot steak to a cold plate is an irreversible process. The effect of this process is to cool down the hot steak and warm up the cold plate, leading to a more uniform distribution of temperature. The heat transfer continues until a state of e
5.2.1 The GM Science Review The review was undertaken by the GM Science Review Panel, chaired by the Government's Chief Scientific Adviser, Sir David King. Its role was to assess the evidence available in the peer-reviewed scientific literature. The panel produced two reports, the first in July 2003 and the second in January 2004. The main conclusions of these reports are listed below. The risk to human health is very low. There is little likelihood of such plan
4.4 Incorporating substantial equivalence into national and international law The concept of substantial equivalence very quickly became important in international trade law. The WTO aims to harmonise national food standards to meet international norms. Under its rules, a country could be penalised if it imposed food standards more stringent than those agreed internationally. In this context, international food standards are set by the Codex Alimentarius Commission (Table 1). In 1996, a report was issued within the Codex framework, which endorsed the principle of subst
4.2 Scientific risk analysis In the context of national and international legislation on the safety of food and animal feed, much of the thinking about assessing risk has come from the experience of developing legislation to cover potentially toxic chemicals. In this regard, the terms ‘risk’ and ‘hazard’ are particularly important. ENTRANSFOOD (European network safety assessment of genetically modified food crops) has defined the terms as follows: 2.2 What is natural? Many critics of GM feel that the techniques reflect an unwelcome form of ‘tampering with nature’. This is a particular concern of some consumers with respect to food. Such a view is sometimes scornfully interpreted as an expression of what is called the ‘naturalistic fallacy’ – a belief that equates morality with naturalness, seeing what is natural as ‘right’. But concerns about GM foods may reflect a more reasoned and defensible position. It might be argued that consumers are n 2.5 Using stars to probe the interstellar medium The effects of interstellar material on starlight can be used to probe the properties of the interstellar medium itself. A few examples are: The presence of particular interstellar atoms or molecules may be determined by identifying the observed spectral lines or bands. The temperature of the gas may be determined from the relative strengths of different lines or bands produced by different energy state changes of the same atom or mol 1.1 Constructing the H–R diagram Three properties which are suitable for comparing stars are temperature, luminosity and radius. However, we don't need all three. Why not? 6 Phylogeny and cladistic analysis In Section 3.3 the point was made that many physiologists consider that desert birds are successful because of their avian physiology, not because of any specific adaptations. While Williams and Tieleman's research on hoopoe larks demonstrated that desert species are capable of flexibility in metabolic rate and evaporative water loss, it suggested that adaptation is important too. The selective advantages of lowered BMR and TEWL for desert birds include reduced energy demand, and lower produc 3.2 Integration of anatomy and behaviour with biochemical and physiological strategies in evaders We know from Section 2.3 that small desert rodents remain cool by staying in their burrows for all or part of the day. Kangaroo rats (Dipodomys spp.; see Figure 20 in Section 2.3) depend on metabolic water as there is little or no water available in their diet of seeds. Kangaroo rats appear to be ill-adapted for 2.2 How animals interact with the environment is affected by their body size Willmer et al. (2000) classify desert animals in terms of the range of body sizes and the rate of evaporation (Figure 8). 2.4 Summary Adaptive hypothermia occurs widely in both mammals and birds, but the ability is scattered throughout different families: even within single families, some species show torpor and some do not, suggesting that the ability may have evolved independently many times. Whereas a number of small birds show a daily, shallow torpor, so far only the poor will has been described as showing extended bouts of torpor comparable to those seen in mammals. Species of birds and mammals that hibernate (Figures 2.1 Degrees of torpor Adaptive hypothermia occurs in at least six distantly related mammalian orders (Table 1) and in several orders of birds. There is a spectrum running from those species which can tolerate a drop in T
b by 2° C for a few hours, to the seasonal deep hibernators which maintain a T
b as low as 4° C for weeks on end. Learning outcomes By the end of this unit you should be able to: define and use, or recognize definitions and applications of, each of the bold terms; give definitions of the terms ‘hibernation’, ‘torpor’ and ‘adaptive hypothermia’, and the three physiological processes that underlie them; give examples of the diversity of the major groups of mammals and birds that contain hibernating species; describe the physiological changes occur
Question 1
Table 1 Groups o
