"On a different time scale, a perceptual mechanism seems to exist that integrates separate successive events into a unit or perceptual gestalt (see Poppel 2009). We do not just perceive individual events in isolation, but automatically integrate them into perceptual units with a duration of approximately 2–3 s (Fraisse 1984; Poppel 1997). For example, while listening to a metronome at a moderate speed, we do not hear a train of individual beats, but automatically form perceptual units, such as 1–2–3, 1–2–3, etc. These are mental constructs—physically speaking, they do not exist. The duration of this temporal integration mechanism, referred to as the subjective present, seems to be limited to 2–3 s (Szelag et al. 1996; Wittmann & Poppel 2000)."

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"The notion that perception and motor behaviour are processed in discrete windows or processing epochs has been conceptualized for some time (White 1963; Poppel 1970; Dehaene 1993; VanRullen & Koch 2003; Fingelkurts & Fingelkurts 2006). These temporal integration units fuse successive events into a unitary experience, ‘snapshots of experience’ or ‘psychological presents’ (Blumenthal 1977), which are characterized by co-temporality, meaning that
events within this time zone have no temporal relationship (Ruhnau 1995). For example, the perception of temporal order of short stimuli in different modalities is only possible if the individual events are separated by at least 20–60 ms (Exner 1875; Hirsh & Sherrick 1961; Kanabus et al. 2002; Fink et al. 2006). f the two events are separated by smaller intervals, an observer is not able to tell which of the two appeared first."

"The term ‘specious present’ was first introduced by the psychologist E.R. Clay, but the best known characterisation of it was due to William James, widely regarded as one of the founders of modern psychology. He lived from 1842 to 1910, and was professor of philosophy at Harvard. His definition of the specious present goes as follows: ‘the prototype of all conceived times is the specious present, the short duration of which we are immediately and incessantly sensible’ (James (1890)). How long is this specious present? Elsewhere in the same work, James asserts ‘We are constantly aware of a certain duration—the specious present—varying from a few seconds to probably not more than a minute, and this duration (with its content perceived as having one part earlier and another part later) is the original intuition of time.’ This surprising variation in the length of the specious present makes one suspect that more than one definition is hidden in James' rather vague characterisation."

THE PSYCHOLOGICAL PRESENT

To perceive is to become aware of stimulation. Awareness of sequence or duration may, at first glance, seem inconsistent with the definition of perceiving. In a mathematical sense, certainly, the present is only a point along the continuum of becoming, an instant when future is transformed into past. Nevertheless, there is indeed a more prolonged psychological present, a brief period during which successive events seem to form a perceptual unity and can be apprehended without calling on memory. There is a perceptual field for time just as there is a visual field. The rate or speed of a sequence determines the limits of the time field.

When a metronome tics two or three times a second, one perceives an integral sequence, becoming aware of a rhythmic auditory series characterized by a perceptually distinct frequency. When the ticks come less often, however—at intervals of three seconds, say—the frequency or sequence no longer is perceived. Each physically discrete sound impulse remains an isolated perceptual event; each tick is no longer perceived as belonging to the same temporal field as the one that follows. Similar effects can be achieved by playing a recording of music or speech at a very slow rate. Music or spoken sentences are recognizable only when their elements (melody, rhythmic patterns, phrase) are presented at an optimal speed that permits significant perceptual unity; that is, only when they belong to the relative simultaneity of the psychological present.

The perceived field of time also depends on the number of stimulus elements presented. When a clock strikes three or four times, one knows without counting that it is three or four o’clock. At noon one must count; the first chimes no longer belong to the psychological present that includes the last. Most people also can repeat a series of letters or numbers they hear, so long as there are no more than seven or eight elements. This ability varies with the degree of perceptual (e.g., semantic) organization among the elements. While most adults can apprehend only about eight letters, they can grasp and repeat without fault sentences of 20 to 25 syllables.