12.6 Distance cues There are two main cues available that allow us to judge the distance to a sound source. The first of these is the sound pressure level. Sound pressure level drops by 6 dB each time the distance that a sound travels doubles. In other words, if the sound pressure level of a sound is 60 dB SPL when its source is 1 m from you, then it will be 54 dB SPL if you move back another metre so that you are now 2 m away from its source. Therefore lower sound pressure levels indicate a greater distance. A
11.5 Summary of sections 8 to 11 In these sections we have described some of the quantitative relationships between the physical dimensions of simple sounds and their subjective psychological dimensions. The physical dimension of intensity, or pressure amplitude, given in decibels (dB), directly affects loudness. Frequency of pressure changes, in hertz (Hz), mainly determines pitch. The lowest threshold value and hence the maximal sensitivity for humans is in the region of 3000 Hz. The quantitative relationship b
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). References 5.3.1 Muscles The rates of muscle contraction and relaxation, and the maximum force generated, are complex enzymatic processes that determine speed of swimming. Ian Johnston of St Andrews University (Johnston, 1989) has compared the maximum tension of muscle fibres isolated from several species of antarctic, temperate-zone and tropical fish (Figure 25). Acknowledgements The content acknowledged below is Proprietary (see terms and conditions) and is used under licence. Grateful acknowledgement is made to the following sources for permission to reproduce material in this unit: Figure 2 Nortier, P. and Soustelle, M. (1987) 'Alumina carriers for automotive pollution control', in Cruecq, A. and Frennet, A. (eds) Catalysis and Automotive Pollution Control, Elsevier Science Publishers; Fi 9.3 Monoamine oxidase A, maltreatment during childhood and later violence One Dutch family was found to have a history of antisocial (aggressive) behaviour. Genetic studies were conducted and a potential culprit gene MAOA, monoamine oxidase A, identified. The aggressive individuals in the family appeared to have a mutant gene which produced no MAOAP, an enzyme involved in the breakdown of certain neurotransmitters, including serotonin. A knockout mouse model, in which the MAOA gene was inactive, was also found to be aggressive, apparently confirming the role of MAO 9.1 The psychological arena The examples in the previous section followed the traditional medical approach, namely that there is a disease, it can be diagnosed (identified), and the cause of the disease, be it viruses, bacteria, pathogens, genes or poisons, can be sought. This section moves away from the medical arena and into the psychological arena, where the symptoms are behavioural. In this case, the symptoms are socially unacceptable behaviour and to the list of causes just mentioned is added family circumstances a 7.8 Summary of Section 7 This section has sought to illustrate the formation of connections between neurons and their targets by exploring a few examples. The picture that emerges is one of cells at different stages of development subjected to a vast array of signals. These signals are the medium through which environmental factors exert their effects. To some of these signals, some cells respond; to other signals, other cells respond. What a cell, a neuroblast, a growth cone actually does is dependent on the combina 6.5 Summary of Section 6 Growth cones respond to proximal and distal cues. The proximal cues in the extracellular matrix or other cells affect adhesion and result in chemotactic guidance. Distal cues are also in the extracellular matrix but they diffuse through it and result in the growth cone either moving towards the source (attractants) or away from it (repellants). These distal cues are chemotropic cues and can have different effects on different growth cones; what may be an attractant to one growth cone may be r 6.3 Directing the growth cone The growth of the growth cone has been likened to the progress of a climber. The climber can only go where there are satisfactory hand and foot-holds and where progress is not blocked by physical obstacles (e.g. overhangs or ice). Furthermore, the climber is looking ahead for the best routes, from the current position to the top. Likewise the filopodia on the growth cones are extending outwards, adhering to the best holds and avoiding physical obstacles (e.g. bone or cartilage). This contact- 5.3 Transcription factors At various places in this unit, reference is made to new proteins being made, or to genes being switched on. The control of gene transcription is a hugely complex area and well beyond the scope of this unit. However, it is helpful to know that for any gene to be switched on, for any new protein to be made (or an old protein replaced), an appropriate transcription factor must be present, and it must couple with an appropriate part of the DNA. In biological terms a transcription factor is a mol 4.4 Summary of Section 4 Two important points emerge from this section. The first is the powerful effect of maternal contact on the development and later behaviour of their charges. In the Feldman study the disadvantages of prematurity were essentially overcome by early maternal contact. The second point is that some behavioural traits really do run in families, without being genetic. The Francis study clearly showed that some aspects of Open Field behaviour were the result of nursing care. 4.2 Licking/grooming-arched back nursing Rat mothers perform a number behaviours towards their pups: they build a nest for their pups, keep them in it and occasionally lick them and nurse them. (Rat fathers have a parental role too but it is not essential and the experimental set-up is simplified by his absence.) Licking occurs predominantly at the time when the dam arches her back and nurses her young, allowing a composite behaviour of licking/grooming-arched back nursing to be identified and recorded. If licking/grooming-arched ba 4.1 Parental behaviour A moment's reflection will convince you that parental behaviour differs from one family to another. The effect that different parental styles have on the development of the recipient offspring is very difficult to establish. In part this is to do with the host of other differences between families, not least their genetics and socio-economic status. But also the difficulty arises because to determine cause and effect requires prolonged and intrusive observations of a sort that is not possible 3.3 Plasticity and permanency The visual system relies on, amongst other things, the exquisitely precise connections between the retina, the lateral geniculate nucleus of the thalamus and the visual cortex. In precocial organisms, i.e. those born or hatched able to see and move about, such as horses and ducks, these connections arise in complete darkness. The information necessary to establish the connections must therefore be in the genome. The question then arises as to whether the environment, visual stimulation in thi 3.2 Small babies Development continues in the womb until birth, which, in humans, is about 38 weeks after conception. (The often quoted duration of pregnancy of 40 weeks is based on pregnancy beginning on the first day of the last menstrual period.) The duration of the period of development before birth, called gestation, is highly variable. It is not possible to determine its full range in the UK, because medical intervention usually prevents pregnancies going beyond about two weeks after the due date, or te 3.1 Introduction We each begin life with a unique genome. As we grow and develop, we are each subjected to a range of factors that influence the way development proceeds. Most of those factors are common to us all, the intracellular and intercellular signals, hormones, birth, milk. But the precise combination and the range and duration of those factors varies between individuals, such as the duration of gestation or the composition and quantity of a mother's milk, for example. In addition we each undergo diff 1.2 The ‘genes and behaviour’ problem Amidst the progressive change to the brain and nervous system that occurs during development, there is one constant, one fixed element; the set of deoxyribonucleic acid, DNA, molecules found in each cell. These molecules are the genetic material, and they store the information for the construction of the organism. The same set of DNA molecules is found in every cell of an organism (its genome). (There are some exceptions to this such as sperm, unfertilised egg and red blood cells, but they ne 1.1 Introduction This unit addresses the question of how the differences between individuals, especially in behaviour, arise during development. Development, the transformation of the single cell, the zygote, into an adult organism with billions of cells, numerous organs and an intricate, functioning nervous system, is one of the most remarkable feats of living systems. The process begins when an egg cell, or ovum, is fertilised by a sperm, or spermatozoon. The resultant single cell, the zygote, divides to pr
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