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РАЗДЕЛ 3. ПСИХОФИЗИОЛОГИЯ
УДК 59.9
Кази Саифуддин Ашок Кумар Шаха Ферджана Ахмед
Департамент психологии, Университет Джаганатх, Дакка 1100, Республика
Бангладеш
E-mail: asoke_saha@yahoo. com
ПОЛУШАРНАЯ ДОМИНАНТНОСТЬ ЗВУКОВРЕМЕННОГО ВОСПРИЯТИЯ В МОЗГЕ ЧЕЛОВЕКА
Prof. Dr. Kazi Saifuddin Dr. Asoke Kumar Saha Farjana Ahmed
Department of Psychology, Jagannath University, Dhaka, Bangladesh
Dhaka 1100, Bangladesh E-mail: asoke_saha@yahoo. com
HEMISPHERIC DOMINANCE OF AUDITORY TEMPORAL PERCEPTION
IN HUMAN BRAIN
Аннотация. Исследовалась полушарная доминантность функции восприятия времени в условиях звукового стимула. Записывались слуховые вызванные потенциалы (СВП) испытуемого, находящегося в сурдокамере. С помощью компьютерных технологий оценивалась величина воздействия слухового стимула на межполушарные различия. Слуховые сигналы (белый шум) смешивались с варьирующимися уровнями звукового давления (УЗД) или с переменным шумом с постоянным интервалом около 1 мс. В результате было обнаружено доминирование СВП в левом полушарии по сравнению с правым полушарием (p < 0.05). Также было обнаружено левополушарное
доминирование латентности СВП (p < 0.01). Делается вывод о том, что левое полушарие человеческого мозга является доминантным для функции звуковременного восприятия.
Ключевые слова: звуковременное восприятие; слуховые вызванные потенциалы; уровень звукового давления.
© Саифуддин Кази, Шаха Ашок Кумар, Ахмед Ферджана , 2015
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|Д| ВЕСТНИК ПГГПУ Серия № 1. Психологические и педагогические науки
Abstract. Hemispheric dominance was tested for only temporal perception when the stimuli were auditory type in human. In an anechoic chamber auditory evoked potentials (AEP) for the single subject were recorded by the summing computer technique to study the magnitude effects of auditory stimuli on the hemispheric differences. Auditory signals (white noise) were propagated with different values of sound pressure level (SPL) or magnitudes with constant rise and fall times about 1 ms. In the results, dominating amplitudes of AEP were found for the left-hemisphere (p < 0.05) than that of the right-hemisphere. Also dominating latencies of AEP were found for the left-hemisphere (p < 0.01) than that of the right-one. Left-hemisphere was concluded as dominating than that of the right one for the auditory-temporal perception in human brain.
Key words: auditory temporal perception duration; auditory evoked potential; sound pressure level.
Introduction
Each part of cerebral hemisphere processes environmental information in a different but complementary manner. Structures perception located in the left hemisphere are assumed to participate in symbolic-logical thinking. Thus, the time perception should be investigated in the context of hemispheric dominance or specialization. Because of the horizontal axis as time is determinant of all material changes on the vertical axis. In connection with this a reversal group was used before to carry out a complementary test in which subjects responded in the first block of experiments with the non-dominant (left) hand and with the dominant hand in the second [11]. Results showed that left hemisphere activity was continuous during the interval-learning stage and with optimal reaction times and remained continuous when estimation values approximated the real interval. In addition, in optimal reaction time and near to optimal time estimation responses, the left side showed lower frequency and alpha ratio than did the right. Results from the reversal group did not differ from those of the first group.
Sperry's experiments demonstrated the existence of lateralization
or hemispheric dominance (Nobelprize.org). However, it should be noted that the study of hemispheric dominance and lateralization is very complex and includes many open questions and inconclusive research. In addition, it should be noted that these instances of lateralization tend to occur in functionally specific and neurologically local fashions, rather than making people "left-brained" or "rightbrained" as a whole [7]. The right hemisphere is dominant in early processing of words in Mandarin while the left is dominant in late processing [9].
The perception of temporal duration was measured against the different auditory background. Subjective time is not isomorphic to physical time [3] the subjective duration of an event can be systematically overestimated, a phenomenon referred to as «time dilation», «time subjective expansion» [16] or «chronostasis» [5; 17]. Time dilation was recently proposed to rely on the predictability of the event to be judged: low probability events (i.e. high unpredictability) would be experienced
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as longer than high probability (i.e. high predictability) events of equal physical duration [16]. Distortions of subjective duration have also been reported in different contexts, namely, at the time of saccade [17; 10] or during voluntary action [12]. An extensive review of literature shows that the duration of an event is not solely experienced on the basis of its temporal properties: attention, arousal and emotional levels, expectancy and stimulus context can all affect the experience of time [6; 19] are related to the hemispheric specialization.
The click-evoked potentials from the human brainstem are currently used in audiology [2] and in neurology (Starr and Anchor, 1975). The average evoked potential to the auditory signal repetitions is determined by the amplitude and latency characteristics of the evoked-wave forms [13; 20] has shown that threshold at 1 kHz falls 10dB for a tenfold increase in duration up to about 200ms. It clearly indicated that greater amplitude and shorter latency are observed in the auditory evoked response as sensation level is raised [14] suggested that the latency of the evoked response decreased with an increase in signal duration because of temporal summation. In this case, amplitude and latency of the concern peaks can be calculated to explain the hemispheric dominance by comparing between the two hemispheres and a similar study was conducted by Saifuddin [15].Though the temporal as well as the spatial factors are fundamental criterion of environment, and purpose of the present study is to obtain basic knowledge about the dominance of temporal factors over the spatial factors in cerebral hemisphere of the human brain.
Methods
Acoustic Signal
The sound as acoustic signal has been defined by four orthogonal factors of the autocorrelation function (ACF) as a prominent signal processor which is expressed by the equation 1 [1].
0(T) = jp + t) dt
(1)
Where, p(t) is the signal (stimulus) at the entrance of the ears is the delay time, and 2T is the integration interval. In such ACF analysis, there are four parameters, namely-
a. the energy represented at the origin of the delay, Ф(0);
b. the amplitude, ф1, between the first peak and the zero crossing number;
c. the structure including the time delay of the first peak, t1. and
d. the effective duration of the envelope of the normalized ACF, те, which is defined by ten percentile delay or at which the envelope of the ACF becomes -10dB.
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The first one (a) was used here as sound pressure level (SPL) in the white noise
signal.
Subject
One subject (34 yr.) participated in this experiment. The male subject with normal hearing level took the conventional seat in the anechoic chamber and push the button when perceive signal duration is longer than the standard signal.
Signal Production
In total four white-noise signals with a constant duration of 4ms each were selected for the both physiological and psychological tests as normal wave form (Figure 1a). The rise and fall times of all signals were controlled by 1ms each. Such rise and fall times were measured based on the -3dB slop (Figure 1b). Four signals with SPL of 50, 60, 70, and 80 dB (A) were used through autocorrelation function (ACF) analyzer in the anechoic chamber.
Physiological Test
Four signals were produced repeatedly by a loudspeaker in the chamber from the horizontal distance about 74+1 cm from the listening position. Right-handed subject was seated on a easy chair under relax session with close eye and no body movement. Two unipolar silver-disk electrodes were attached to the left and right temporal areas labeled as T3 and T4 respectively, according to the international 1020 system (Jasper, 1958). The reference electrodes were located on the right and left earlobes and connected together. Ground electrode was placed at the center of the forehead and Silver electrodes (7 mm diameter) with electrolytic paste also used. In this session, electrical signals were amplified using a polygraph with a bandwidth of 0.3 50 60 Hz (Nihon Kohden Type 7109).
Figure 1: Wave form of sound signal: (a) normal slop, and (b) -3dB slop of rise and fall of the white noise
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РАЗДЕЛ 3. ПСИХОФИЗИОЛОГИЯ
Forty responses were averaged online with a signal average (Nihon Kohden Type ATAC-450). The data from two channels of T3 and T4 were averaged simultaneously, and the data on four SPL conditions (50, 60, 70 and 80 dBA) were also averaged independently. The amplitudes were calibrated using a 50v calibration signal with an EEG amplifier.
Psychological Test
Different four paired-acoustic signals of white noise were presented in the by paired-comparison test through four sessions. First signal was white noise with constant duration 150ms and constant SPL 50dBA. Second signals of ten white noises with ten durations (140, 150, 160, 170, 180, 190, 200, 210, 220 and 230ms) were used under four SPL conditions (50, 60, 70 and 80dBA) separately through four sessions. Rise and fall times of all signals were kept constant 1ms. The intra-pair and inter-pair presentation gaps were 1 and 3s, respectively. Each pair was repeated twenty times in each session. Subject judged whether second signal is longer than the first one and pushed button (Stanley, 1998). Subject went through four sessions with six different SPL conditions maintaining 10m rest time between two sessions and same setting position as before.
Results
The auditory evoked potentials (AEP) were recorded from the T3 and T4 positions of the skull. In this situation a short signal of about 4s duration was repeated alternatively as similar to the paired-comparison tests. The AEP responses were recorded and averaged of the 50 repetitions for each signal with different SPLs. Using the summation technique of the computer found wave-forms are shown in the Figure 2.
Figure 2: Averaged AEPs of the left and right hemispheres under four SPLs conditions: (a) 50dB, (b) 60dB, (c) 70dB, and (d) 80dB. Unit is defined as
50v = 0.614674
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In this wave forms of the physiological evoked, both the peaks as ‘P’ and ‘N’ with their sequential numbers were calculated on the basis of their latencies on horizontal axis and on the basis of amplitudes on the vertical one (Figure 3a and 3b). Here, P1, P2, P3, N1 and N2 were considered because of its concern with the psychological correlates.
Cumulative frequencies of duration judgments by the subject with four parameters of different SPL condition presented first in each pair shown in Figure 3(c). The 50 % line of the duration judgments when reference duration is 150ms was defined as threshold. On the 50 % line data were found 165.0, 170.0, 225.0, and 238.0ms, respectively (longer than 150ms are: 10.0, 13.3, 50.0, and 58.7 %, respectively) when white noises SPLs were: 50, 60, 70, and 80dBA.
Figure 3: (a) Amplitudes (0: left-hemisphere, □: right-hemisphere, and -: average); (b) Latencies (o: N1-left-hemisphere, x: N2-left-hemisphere, •: N1-right- hemisphere, ■: N2-right-hemisphere, and -: average); and (c) 50% line of psychometric functions
Discussion
The experiment recorded the amplitudes and latencies of the auditory evoked potential of the brain established exclusively on the onset of signal amplitude. In the Figure 1, rise and fall times were controlled by considering density of energy. In the Figure 2, eight averaged wave forms are shown by means of two hemispheres and four different SPLs. The eight waves are finally averaged and shown in the Figure 3 (a and b) in which, graphic values (Figure 3a) of left hemisphere are always higher (means dominating) than that of the right hemisphere. Side by side in the Figure 3b, latencies for N1 and N2 both are found in the left hemisphere with higher values than that of those N1 and N2 in the right hemisphere. In the Figure 3c, averaged psychometric function indicates the higher values of perceived duration when the
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SPL is higher significantly. Subjective study has been taken here because of evidence of the subjects’ attentive judgments between two signal durations which is obtained in the AEP.
By considering all the factors and effective conditions of this experiment it can be concluded that for the time perception (duration judgment) left hemisphere plays a dominating rolls than that of the right hemisphere of the human brain. Thus the hemispheric dominance is proved experimentally for subjective time duration of human brain.
References*
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10. Morrone, M.C., Ross, J. and Burr, D. (2005). Saccadic Eye Movements Cause Compression of Time as Well as Space. Nature Neuroscience, 8, 950-954.
11. Neville, H.J. (1997). Neural Systems Mediating American Sign Language: Effects of sensory experience and age of acquisition. Brain and Language, 57, 285-308.
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*Список литературы к данной статье оформлен в соответствии с требованиями зарубежных стандартов (APA).
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13. Paul, H.S. and Howard, C.J. (1968). Effects of Signal Duration and Rise Time on the Auditory Evoked Potential. Journal of Speech and Hearing Research, 11, 301-306.
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17. Yarrow, K., Haggard, K., Heal, R., Brown, P. and Rothwell, J.C. (2001). Illusory Perceptions of Space and Time Preserve Cross-saccadic Perceptual Continuity. Nature, 302-305.
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