Buonomano points to the plurality of uses of the term „time.“ For his purposes, he distinguishes three meanings: natural time (time as a medium or dimension of nature), clock time (the time of the physicist), and subjective time (the subjective sense of temporal flow and duration produced by the brain). As a neuroscientist, he is interested in the questions of how and why the human brain generates an intense sense of the passage of time. In his view, the brain is a time machine that tells time, predicts the future, and, moreover, enables mental time travel. He emphasizes that only the ability to mentally travel into the future has enabled humans to make stone tools or understand the connection between sowing seeds and future survival.

Not only the brain, but living beings in general, generate autonomous physiological processes that internally „tell“ time at the level of cells, tissues, and organisms. These so-called biological clocks differ significantly from technically manufactured clocks. While atomic clocks tell time nonspecifically over many orders of magnitude, biological clocks are magnitude-specific. The brain possesses a multitude of more or less autonomous, specific mechanisms that generate internal standards for the passage of time over a range of twelve orders of magnitude, from the millisecond range to the determination of the seasons. Buonomano speaks of a „different-clocks-for-different-time-scales strategy“ or a „multiple clock principle.“ Therefore, for example, the circadian clock has no direct influence on the ability to estimate time intervals in the second or minute range: It has neither a second nor a minute hand. It has only an indirect influence in that it shapes the performance of all physiological and cognitive abilities, including all other biological clocks, throughout the day.

Buonomano distinguishes between prospective time determinations – extending from the present into the future, e.g., measured with a stopwatch – and retrospective time determinations – extrapolated from the present back into the past, e.g., resulting from known, ending sequences. In the first case, nothing can be said about times before the stopwatch starts, in the second case, nothing about times after the sequence ends. Both forms of time determination are part of everyday life, but both are processed differently by the brain. Prospective time determination is a genuine brain function; retrospective time determination is not a time measurement at all, but rather an inference from remembered events.

From the prospective perspective, waiting times with few events appear long, and periods with rich experiences appear short. From the retrospective perspective, the waiting time remembered with few events appears short, and the period with rich experiences appears long. This connection between remembering and the sense of time has been experimentally investigated and confirmed. It is blamed for the pronounced context-dependent misjudgments of durations in everyday situations, but can also be manipulated, for example, when perceived waiting times appear shorter due to music. Furthermore, it can lead to differences between individual time expectations and standardized („objective“) time courses (time illusions).

Buonomano distinguishes between the precision and accuracy of clocks. Precision refers to the average deviation of the oscillator over many cycles; accuracy refers to the correlation of the average period with respect to an external reference. The circadian clock is comparatively accurate, with deviations from the 24-hour daily cycle tending to be plus two percent in diurnal animals and minus two percent in nocturnal animals. The precision of biological clocks, with deviations tending to be one percent of the period, is better than any clock manufactured before the 17th century, until Christiaan Huygens built the first high-precision pendulum clocks.

Biological clocks are good oscillators, but unlike the use of engineered clocks, living organisms are barely capable of counting periods. While the former are primarily used to determine the duration of events shorter than the period (infraperiod timing), the latter are primarily used to measure durations spanning many periods (supraperiod timing). The circadian clock reveals when it is morning or evening, but not how many days have passed. Like an hourglass, it must be reset after each expiration. Consequences such as jet lag are due to the fact that such a reset—unlike a technically manufactured clock—is not possible instantly because it is highly phase-dependent.

Biological clocks do not convey a sense of time; other central nervous mechanisms exist for this. Buonomano speaks of a sixth sense, which, however, is not based on a sensory organ such as the eye or ear, because time is not a physical property like light waves or pressure fluctuations. Nevertheless, the brain not only tells time but also conveys a sense of the passage of time. However, perceived time can deviate significantly from the objective clock time, which is not surprising given that almost all subjective experiences, including the perception of color and pain, as well as bodily sensation, are shaped by context, knowledge, attention, and drug influences. Our sense of time is indeed quite imprecise and strongly influenced by context.

Experiments with chronopharmacological substances suggest that there is neither a dominant regulatory neurotransmitter nor a „master internal clock“ that globally fixes or regulates the sense of time. Statements about perceived time dilation or contraction conventionally refer to external timekeepers, even if it is the (hypothetical) internal clock whose speed is modified—e.g., under the influence of drugs. Overall, disturbances in the perception of time seem to be the rule rather than the exception. Subjects tend to overestimate durations. Furthermore, it may be that the neural labeling of events as fast or slow is independent of the rate at which the brain actually processes time determinations.

For the generation and understanding of speech and music, time means the same as space does for the recognition of visual objects, except that the relevant linguistic and musical features must be integrated over time, rather than being present simultaneously as in the recognition of objects. Pauses and speech rate structure word references and sentence meanings, and different voice onset times discriminate between similar-sounding syllables (phonemes). Emotions and intentions are also expressed in the temporal progression and temporal characteristics of speech (prosody). Overall, the brains of listeners and speakers alike must solve a series of complex, hierarchically structured (sensorimotor) timing problems – a task that is far beyond the capabilities of a simple clock-like device.

Speech and music depend on the speed of the process and lose their intelligibility if they are slowed down or accelerated too much. Subsecond timing is a prerequisite for „seeing both the forest and the trees.“ Slowing down speech and lengthening pauses between words makes language learning easier for both adult and toddler learners. Both humans and songbirds have a critical period during development for the acquisition of vocalizations.

A large neural network can encode not just one, but many event-specific timers. Motor coupling can trigger specific movements at specified times. Using the example of C14 dating, one of the most reliable methods for retrospective time determination, Buonomano explains how the statistical probability of a decay event for a single atom allows estimates of the required time to be obtained from the number of atoms affected by it – via the half-life: The larger the number (population) of observed atoms, the more precise the time determination, even though nothing can be said about the decay of a single atom.

He uses the example as an analogy to population-based clocks in the brain, which refer to the subpopulation of active neurons at a given time. Complex dynamic nonlinear and feedback neural networks are chaotic but can nevertheless generate reproducible activity patterns. The interrelationships are not understood. But it is possible to tune the strength of the synaptic connections of an artificial neural network so that it is able to generate reproducible output patterns even in the face of disruption. The information that generates the output pattern is everywhere and nowhere. Every circuit element contributes, but no single one is required. „The pattern is an emergent property: the whole is larger than the sum of the parts.“

The brain can use the dynamics of neural networks to establish correlations between internal network states and changes in the environment. The tapping of a finger every second means nothing other than synchronizing brain processes with a clock. Ultimately, this is all that is meant when it is said that the brain tells time.

Neurophysiological experiments indicate that spatial and temporal experiences are interdependent. It is assumed, and evolutionarily justified, that temporal classifications rely on spatial forms of presentation. This hypothesis is supported by the fact that people often use spatial terms when talking about time, relying on – culturally influenced and perspective-based – metaphors of the spatialization of time or of time as a moving object. Linguistically speaking, spatial metaphors are used more frequently to talk about time than vice versa. However, the use of spatial metaphors is also very common in many other, especially social, contexts.

Using the example of instruments on a concert stage, Buonomano explains the interdependence of spatial and temporal perception. Acoustic and visual stimuli that reach the sensory organs with different delays can, in certain contexts, be perceived as simultaneous (psychological relativity of simultaneity). Despite a resolution of approximately 20 milliseconds, the brain interprets acoustic and visual stimuli from the same source with a delay of up to 100 milliseconds as an integrated, unified perception (temporal window of integration, which is not fixed but adaptable) – but only if the visual signal is registered before the acoustic one!

Consciousness does not provide an actual image of the world, but rather a highly processed interpretation of reality. Buonomano points out, for example, that humans are blind during phases of blinking and eye movement without knowing it. Estimates suggest that over the course of a day, we miss an hour’s worth of information without realizing it. Furthermore, subsequent events can influence or distort the temporally integrated conscious representation of preceding events. In language, for example, subsequent predicates can semantically define preceding subjects.

Consciousness does not reflect the actual temporal structure of events; rather, the subconscious continuously processes the incoming perceptual streams, waiting for critical moments before sending a refined representation to consciousness (backward editing in time). The time lag until a usually very selective and highly processed representation becomes conscious (conscious present) can last longer than a third of a second.

The brain constantly extracts all the patterns it can find from perceptions and experiences in order to make sense of the world around us. In particular, it draws on past experiences to draw conclusions about time and space. According to Buonomano, the evolutionarily developed function of memory is not to document the past, but to generate a basis for orientation for future predictions and decisions about action. The brain is a prediction or anticipation machine that continually explores possible futures, only occasionally setting time markers that allow episodic memories to be located on the timeline.

„The brain cuts, pauses, and pastes the reel of reality before feeding the mind a convenient narrative of the events unfolding in the world around us. Yet unless we stop to think about it, we are left with the impression that our conscious experiences reflect an instantaneous play-by-play account of reality.“

Literature:

Buonomano Dean (2017), Your Brain Is a Time Machine

Buonomano Dean (*1965):

Neuroscientist at the University of California, Los Angeles (UCLA)
Author of popular science books

Keywords:

Plurality of concepts of time, Multiple Clock Principle

Kommentare