Synchronization is the coordination of events to operate asystem in unison. For example, theconductor of an orchestra keeps the orchestra synchronized orin time. Systems that operate with all parts in synchrony are said to besynchronous orin sync—and those that are not areasynchronous.
Time-keeping and synchronization of clocks is a critical problem in long-distance ocean navigation. Beforeradio navigation andsatellite-based navigation, navigators required accuratetime in conjunction with astronomical observations to determinehow far east or west their vessel traveled. The invention of an accuratemarine chronometer revolutionized marine navigation. By the end of the 19th century, important ports providedtime signals in the form of a signal gun, flag, or droppingtime ball so that mariners could check and correct their chronometers for error.
Synchronization was important in the operation of 19th-century railways, these being the first major means of transport fast enough for differences inlocal mean time between nearby towns to be noticeable. Each line handled the problem by synchronizing all its stations to headquarters as a standardrailway time. In some territories, companies shared a single railroad track and needed to avoid collisions. The need for strict timekeeping led the companies to settle on one standard, and civil authorities eventually abandoned local mean time in favor of railway time.
Inelectrical engineering terms, for digital logic and data transfer, asynchronous circuit requires aclock signal. A clock signal simply signals the start or end of some time period, often measured in microseconds or nanoseconds, that has an arbitrary relationship to any other system of measurement of the passage of minutes, hours, and days.
In a different sense, electronic systems are sometimes synchronized to make events at points far apart appear simultaneous or near-simultaneous from a certain perspective.[a] Timekeeping technologies such as theGPS satellites andNetwork Time Protocol (NTP) provide real-time access to a close approximation to theUTC timescale and are used for many terrestrial synchronization applications of this kind.
A mechanical demonstration of synchronization of oscillators:metronomes, initially out of phase, synchronize through small motions of the base on which they are placed
Synchronization of multiple interactingdynamical systems can occur when the systems areautonomous oscillators. Poincaré phase oscillators are model systems that can interact and partially synchronize within random or regular networks.[1] In the case of global synchronization of phase oscillators, an abrupt transition from unsynchronized to full synchronization takes place when the coupling strength exceeds a critical threshold. This is known as theKuramoto modelphase transition.[2] Synchronization is an emergent property that occurs in a broad range of dynamical systems, including neural signaling, the beating of the heart and the synchronization of fire-fly light waves[3][4]. A unified approach that quantifies synchronization in chaotic systems can be derived from the statistical analysis of measured data.[5]
Synchronization and global synchronization phenomena play essential role in the field of Network Physiology[6][7] with focus on whole-body research to understand the mechanisms through which physiological systems and sub-systems — from sub-cellular, metabolic and genomic scale to cellular and neuronal networks, to organs and the organism level — synchronize their dynamics to coordinate functions and generate distinct physiological states in health and disease. Amplitude, frequency, and phase synchronization, as forms of coupling and interaction, underlie biological/physiological network mechanisms through which global states, functions and behaviors emerge at the system and organism level[3][4]. Synchronization has been reported across physiological systems and levels of integration, including cardio-respiratory coupling[8][9]; maternal-fetal cardiac phase-synchronization[10][11]; brain blood flow velocity vs. peripheral blood pressure in stroke[12]; synchronization in neuron synaptic function[13]; organ networks[14][15]; EEG-synchronization and EEG-desynchronization in NREM and REM sleep[16][17]; brain waves synchronization and anti-synchronization during rest, exercise, cognitive tasks, sleep and wake[18][19][20][21]; cortio-muscular synchronization[22][23]; synchronization in pancreatic cells and metabolism[24][25][26]; inter-muscular muscle fibers synchronization in exercise and fatigue[27][28]; neuromodulation and Parkinson's, dystonia and epilepsy[29][30][31][32]; circadian synchrony of sleep, nutrition and physical activity[33].
In cognitive neuroscience, (stimulus-dependent) (phase-)synchronous oscillations of neuron populations serve to solve the generalbinding problem. According to the so-called Binding-By-Synchrony (BBS) Hypothesis[34][35][36][37][38][39][40] a precise temporal correlation between the impulses of neurons ("cross-correlation analysis"[41]) and thus a stimulus-dependent temporal synchronization of the coherent activity of subpopulations of neurons emerges. Moreover, this synchronization mechanism circumvents thesuperposition problem[42] by more effectively identifying the signature of synchronous neuronal signals as belonging together for subsequent (sub-)cortical information processing areas.
In cognitive science, integrative (phase) synchronization mechanisms in cognitive neuroarchitectures of modernconnectionism that include coupled oscillators (e.g."Oscillatory Networks"[43]) are used to solve thebinding problem of cognitive neuroscience in perceptual cognition ("feature binding") and in language cognition ("variable binding").[44][45][46][47]
There is a concept that the synchronization of biochemical reactions determines biologicalhomeostasis. According to this theory, all reactions occurring in a living cell are synchronized in terms of quantities and timescales to maintainbiological network functional.[48]
Synchronization of movement is defined as similar movements between two or more people who are temporally aligned.[49] This is different from mimicry, which occurs after a short delay.[50]Line dance andmilitary step are examples.
Muscular bonding is the idea that moving in time evokes particular emotions.[51] This sparked some of the first research into movement synchronization and its effects on human emotion. In groups, synchronization of movement has been shown to increase conformity,[52] cooperation and trust.[53][failed verification]
Indyads, groups of two people, synchronization has been demonstrated to increase affiliation,[54] self-esteem,[55] compassion and altruistic behaviour[56] and increase rapport.[57] During arguments, synchrony between the arguing pair has been noted to decrease; however, it is not clear whether this is due to the change in emotion or other factors.[58] There is evidence to show that movement synchronization requires other people to cause its beneficial effects, as the effect on affiliation does not occur when one of the dyad is synchronizing their movements to something outside the dyad.[54] This is known as interpersonal synchrony.
There has been dispute regarding the true effect of synchrony in these studies. Research in this area detailing the positive effects of synchrony, have attributed this to synchrony alone; however, many of the experiments incorporate a shared intention to achieve synchrony. Indeed, the Reinforcement of Cooperation Model suggests that perception of synchrony leads to reinforcement that cooperation is occurring, which leads to the pro-social effects of synchrony.[59] More research is required to separate the effect of intentionality from the beneficial effect of synchrony.[60]
Synchronization is important indigital telephony, video anddigital audio where streams of sampled data are manipulated. Synchronization of image and sound was an important technical problem insound film. More sophisticated film, video, andaudio applications usetime code to synchronize audio and video.[2] In movie and television production it is necessary to synchronize video frames from multiple cameras. In addition to enabling basic editing, synchronization can also be used for3D reconstruction[61]
Arbiters are needed in digital electronic systems such asmicroprocessors to deal with asynchronous inputs. There are also electronic digital circuits calledsynchronizers that attempt to perform arbitration in one clock cycle. Synchronizers, unlike arbiters, are prone to failure. (Seemetastability in electronics).
Encryption systems usually require some synchronization mechanism to ensure that the receiving cipher is decoding the right bits at the right time.
Automotivetransmissions containsynchronizers that bring the toothed rotating parts (gears and splined shaft) to the same rotational velocity before engaging the teeth.
Some systems may be only approximately synchronized, orplesiochronous. Some applications require that relative offsets between events be determined. For others, only theorder of the event is important.[1]
^Ivanov, Plamen Ch.; Bartsch, Ronny P. (2014), D'Agostino, Gregorio; Scala, Antonio (eds.), "Network Physiology: Mapping Interactions Between Networks of Physiologic Networks",Networks of Networks: The Last Frontier of Complexity, Cham: Springer International Publishing, pp. 203–222,Bibcode:2014nnlf.book..203I,doi:10.1007/978-3-319-03518-5_10,ISBN978-3-319-03518-5
^Singer, W. (1999). Neuronal synchrony: A versatile code for the definition of relations. Neuron, 24, 49-65.
^Singer, W. (1999a). Binding by neural synchrony. In R. A. Wilson & F. C. Keil (eds.): The MIT encyclopedia of the cognitive sciences (pp. 81-84). Cambridge, MA, London: The MIT Press.
^Singer, W. (2009a). Consciousness and neuronal synchronization. In S. Laureys & G. Tononi: The neurology of consciousness: Cognitive neuroscience and neuropathology (pp. 43-52). Amsterdam: Elsevier.
^Singer, W. (2009b). Neural synchrony and feature binding. In L.R. Squire (Ed.) Encyclopedia of Neuroscience. Vol. 6 (pp. 253-259). Oxford: Academic Press.
^Singer, W. (2013a). The neuronal correlate of consciousness: Unity in time rather than space? Neurosciences and the Human Person: New Perspectives on Human Activities Pontifical Academy of Sciences. Scripta Varia. Vol. 121. Vatican City. 2013. From: www.casinapioiv.va/content/dam/accademia/pdf/sv121/sv121-singer.pdf
^Singer, W. (2013b). Cortical dynamics revisited. Trends in Cognitive Sciences 17, 616-626.
^Singer, W. (2018). Neuronal oscillations: unavoidable and useful? European Journal of Neuroscience 48, 2389-2399.
^Engel, A. K., König, P., Gray, C. M. & Singer, W. (1990). Stimulus-dependent neuronal oscillations in cat visual cortex: Intercolumnar interaction as determined by cross-correlation analysis. European Journal of Neuroscience, 2, 588-606.
^Malsburg, C. von der (1999). The what and why of binding: The modeler's perspective. Neuron, 24, 95-104.
^Werning, M. (2012). Non-symbolic compositional representation and its neuronal foundation: Towards an emulative semantics. In M. Werning, W. Hinzen & E. Machery (eds.), The Oxford handbook of compositionality (pp. 633-654). Oxford University Press. Oxford.
^Maurer, H. (2021).Cognitive science: Integrative synchronization mechanisms in cognitive neuroarchitectures of the modern connectionism. CRC Press, Boca Raton/FL,ISBN978-1-351-04352-6.doi:10.1201/9781351043526.
^Bechtel, W. & Abrahamsen, A.A. (2002). Connectionism and the Mind: Parallel Processing, Dynamics, and Evolution in Networks. 2nd Edition. Blackwell Publishers, Oxford.
^Richardson, Michael J.; Marsh, Kerry L.; Schmidt, R. C. (1 February 2005). "Effects of visual and verbal interaction on unintentional interpersonal coordination".Journal of Experimental Psychology. Human Perception and Performance.31 (1):62–79.CiteSeerX10.1.1.176.8093.doi:10.1037/0096-1523.31.1.62.ISSN0096-1523.PMID15709863.
^Dong, Ping; Dai, Xianchi; Wyer, Robert S. (1 January 2015). "Actors conform, observers react: the effects of behavioral synchrony on conformity".Journal of Personality and Social Psychology.108 (1):60–75.doi:10.1037/pspi0000001.ISSN1939-1315.PMID25437130.
^abHove, Michael J.; Risen, Jane L. (2009). "It's All in the Timing: Interpersonal Synchrony Increases Affiliation".Social Cognition.27 (6): 949.doi:10.1521/soco.2009.27.6.949.
Media related toSynchronization at Wikimedia Commons