3.4 Specialisation within language areas: brain scanning Is there any evidence from the undamaged brain that the view derived from aphasia is indeed correct? The most useful methodologies here use either PET or functional MRI (fMRI) scanning to establish which parts of the brain are active in particular tasks. The difficulty is that a standard linguistic task, such as understanding a sentence's meaning, involves phonology and syntax and semantics, and thus is not helpful when trying to tease out which of these subtasks happens in which areas.
2.5 From phoneme to sentence structure: the syntactic problem In the vervet monkey system, calls stand by themselves. Thus there is no syntax. Syntax can be thought of as working like road traffic rules do. It doesn't much matter which side of the road you drive on, as long as there is some clear convention. Similarly in (13), it is necessary to understand the difference between (13a) and (13b) without ambiguity, by having some rule or other about which noun phrase comes first. England may differ from most of the rest of the world in terms of the side o
2.3 From ear to phoneme: the phonological problem The phonological problem is the problem of knowing which units (words, calls) are being uttered. The speech signal is a pattern of sound, and sound consists of patterns of minute vibrations in the air. Sounds vary in their frequency distribution. The sound of a flute playing is relatively harmonic. This means that the energy of the sound is concentrated at certain frequencies of vibration. A plot of the energy of a sound against the frequency at which that energy occurs is called a spe
2.2 Generativity and duality of patterning Let us now reconsider the sentence you heard in the imaginary scenario at the beginning of this unit. Here it is again. (1)  My dad's tutor's no joker, and he told me the TMA's going to hit home with a bang. 11.3 Frequency selectivity In preceding sections we examined two ways in which the auditory system may code frequency information: the place theory and phase locking. In this section we will look at the psychophysical evidence for place coding on the basilar membrane by examining the ability of the auditory system to resolve the components of sinusoidal waves in a complex sound – a phenomenon known as frequency selectivity. The perception of a sound depends not only on its own frequency and intensity but also o 10.2 The relationship between loudness and intensity The loudness of an auditory stimulus is a psychological, not physical attribute of the stimulus. The physical attribute of sound that is most closely correlated with loudness is intensity. So loudness is the listener's subjective description of the intensity of the stimulus. As you know, we are not equally sensitive to sounds of all frequencies so perceived loudness of a tone in fact depends on frequency as well as intensity. Two sounds can have the same physical sound pressure levels but if 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 5.2 Frequency code Although the evidence for the place theory of frequency coding is compelling, there is some question as to whether the tuning curves obtained from neurons in the auditory nerve provide a mechanism for frequency discrimination that is fine enough to account for behavioural data. People can detect remarkably small differences in frequency – in some cases as small as 3 Hz (for a 1000 Hz signal at moderate intensity). What accounts for this ability? As early as 1930, the American experimental p 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 2.1 Structure and function of the outer and middle ear Figure 1 is a diagram of the human ear. The outer ear consists of the visible part of the ear or pinna, the external auditory canal (meatus), and the tympanic membrane (tympanum) or eardrum. The human pinna is formed primarily of cartilage and is attached to the head by muscles and ligaments. The deep central portion of the 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 2.6.2 End-of-unit questions Express the following numbers using scientific (powers of ten) notation: (a) 2.1 million (b) 36 000 (c) 1/10 (d) 0.00005 2.3.1 Thermodynamics and entropy The first half of the nineteenth century was a period of great economic and industrial growth. The steam engine, invented in the previous century, was becoming increasingly common in locomotives, mines and factories; power was becoming available on demand. A major priority for engineers was to produce more efficient engines, in order to deliver more useful power for less expenditure on fuel. Thermodynamics emerged as a study of the basic principles determining energy flows and the effi 5.3 GM Nation? The public debate The key objective of the national dialogue on GM was to allow the exchange of views and information – members of the public would presumably learn more about the issues; experts and policy makers would learn more of the reasoning behind the public's concerns. 4.7 Safety assessment today At the time of writing (2006), the descriptions of safety assessment for GM crops and derived products are far more rigorous than the vague prescriptions offered in the early 1990s (see Figure 2). This might be seen as an inevitable development as scientific knowledge increases and technology improves. However, that would only be part of the story. A fully rounded appraisal of the evolution of safety assessment in this field would have to acknowledge the huge part that both the direct critici 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: 4.1 Introduction Pusztai and his team were attempting to develop suitable tests to assess the safety of GM potatoes. Typically, testing the safety of GM food involves comparing its composition and/or its effects with that of the conventionally produced food it most closely resembles. We have seen that such comparisons were at the heart of Pusztai's work. The comparison of GM and conventional crops and food has led to the so-called principle of substantial equivalence, which has been used extensiv 3.2 Communicating Pusztai's findings In mid-1998, the Rowett Institute released a succession of press releases describing Pusztai's findings. The safety, or otherwise, of GM foods was a hot issue at the time and his preliminary findings gained widespread publicity. Pusztai gave an extended interview to the World in Action TV programme ‘Eat up your genes’, broadcast in August 1998. He described some of his experiments and outlined his interpretations in ways that helped shape the general tone of the programme, which was highl 2.4.1 The second generation of GM crops Much of the present-day debate about GM plants centres around the existing range of GM crops, most of which have been engineered for herbicide tolerance or insect resistance (covered in unit S250_1 Gene manipulation in plants). One of the implications of this narrow commercial focus is that the benefit that such crops would bring, other than to those multinational companies that produce them, is by no means clear. Weighing up their value on some form of ethical scales might be unlikely 2.4 Can GM crops feed the world? The issue of global food security is at the heart of many of the ethical issues related to GM technology. United Nations population scientists estimate that the world's population will increase by 2 billion over the next 30 years, posing huge challenges for global food production. More than 842 million people are currently chronically hungry. Proponents of GM crops argue that further development of this technology is vital to meet this challenge. However, a more equal distribution of ex
Activity 2
Question 8
Question 16
