In the previous post, I argued that the different mechanisms in the brain that underpins our ability to perceive time are fragmented. By fragmented I mean that there are several dimensions along which timekeeping mechanisms can dissociate - that the different representations that the timekeeping mechanisms give rise to can be selectively intervened upon along, as I argue, at least five dimensions. These are the dimensions of 1. timescales, 2. modalities, 3. sensory feature type, 4. temporal property types, and 5. temporal judgments.
But our perception of time does not seem to be fragmented across these five dimensions of experience. Our experience of Time seems to be represented in the same way across all timescales (milliseconds to seconds to minutes), all sensory features (movement, colour, etc.), modalities (vision, touch, etc.), all temporal property types (duration, temporal order), and all temporal judgments (our belief that something occurs synchronously or in sequence).
In other words, our perception of time seems to be highly unified in experience, in spite of the fact that the mechanisms underlying time perception are highly fragmented.
How do we explain this perceived temporal unity of our experience?
Let’s say that to explain the perceived temporal unity of time, we must explain two perceptual capacities (localisation and comparability):
1 Localisation can be understood as how events seem to be located in time relative to a specific anchored moment, the moment we live in at every waking moment. Some events seem to have occurred in the past, and some have yet to occur, but they all occur in the past or the future relative to this moment.
2 Comparability can be described as the way we seem to be able to effortlessly compare temporal properties across modalities and timescales. How we compare temporal properties picked up from auditory and temporal properties from visual cues is easy and requires no real translation.
Today we will consider two different approaches: The ‘internal clock approach’, and the ‘mirroring approach’. As these two theories can be taken to explain these two aspects of our experience of time and thus the perceived temporal unity of our experience:
The internal clock approach
According to internal clock approaches time is represented by an internal faculty in the brain. The different modalities of the brain are in charge of processing all the sensory inputs such as visual, auditory, olfactory, tactile, and gustatory stimuli. These are represented and then they stream through the brain’s internal timing device - The internal clock.
The internal clock then attributes a temporal property to sensory stimuli (e.g., the internal clock determines how long the represented sound has lasted).
The most standard internal clock approach is the scalar expectancy theory (SET). SETs employ three pieces of machinery (i) a supramodal pacemaker-accumulator clock (ii) a memory store, and (iii) a decision/comparator mechanism, to explain the unity of time perception.
The way it supposedly works is that the pacemaker pulses at a stable rate and the pulses are then counted by an accumulator. The number of pulses counted during some interval then provides a quantification of the duration of that interval. In this way, the internal clock tracks the timing of the represented sensory features that stream through this internal clock.
The accumulated pulses of the sensory features of one event are then compared to the accumulated pulses of the sensory features of another event (that is stored in the memory store) by some comparison mechanism. This comparison then results in a relative duration judgment about whether the duration of the event just experienced was relatively longer, shorter, or equal to the stored event.
With this story about how temporal properties are attributed to sensory features of events by a single system, the internal clock can easily explain the two perceptual capacities connected to the perceived unity of time.
Localisation is explained by the fact that the internal clock mechanism provides a common temporal ordering. There is only one system that attributes temporal properties and therefore only one timeline within which temporal properties can be located. The temporal property that is being attributed at every waking moment corresponds to the moment we are experiencing.
Comparability is ensured by temporal properties all being of the same kind. Since temporal properties are attributed to events as a single internal clock there will be no modality variation in temporal properties and thus no comparability issues.
The internal clock approach thus seems to account for the perceived temporal unity of experience.
What about the mirroring approach?
The mirroring approach
In contrast to internal clock approaches, the mirroring approach argues that temporal properties are automatically attributed to experienced sensory features the moment they are represented by the sensory mechanism responsible for processing that sensory feature.
Imagine that we turn our head to face a red wall. According to the mirroring approach, we represent the colour red the moment the brain finish processing the colour. So if it finishes processing the red colour at 11:02:12, then we will consciously represent that colour to have occurred in front of us at 11:02:12.
Mirroring approaches states the moment in time at which a sensory feature is represented in experience is identical to the temporal content that we represent.
In other words, the temporal properties of the act that realise the experience we enjoy covary with the temporal properties of our experience itself. Such accounts provide an intuitive and elegant explanation of the two perceptual capacities of the perceived unity of time.
Let us first consider localisation. The local sensory processes responsible for representing various sensory features occur at specific moments in the world, and because the events of the world occur within a single timeline, the act of mirroring explains why we experience these sensory features as occupying a single timeline. Our perception of a single timeline is inherited from the fact that our representations occur within the timeline of the world.
Comparability can also be explained. The representing activity of different representational processes attributes temporal properties to the individual representation of different sensory features, simply by the means of representing a feature. An overarching system can then keep track of temporal properties of the different represented sensory features, simply by keeping track of when they have been processed. Comparison of the time when different sensory features occur in the environment is then simply a job of comparing these temporal properties attributed to the sensory features.
The mirroring approach thus also seems to be able to account for the perceived temporal unity of experience.
A commonality between the two approaches
These two theories, the internal clock approach and the mirroring approach account for the perceived temporal unity of experience by positing a theory of time perception where the temporal properties we represent are of a unitary kind. And so the integration of these temporal properties straightforwardly leads to the perceived unity of time.
A good motivation for assuming that time perception is unified in ways that accord with one of these two theories is that the temporal properties that we perceive seem to be so intimately related to one another.
With this assumption in the bag, then to explain the apparent unity of time perception you just have to find a way that the brain translates the temporal properties of sensory features into a common code and then add a comparison mechanism that can compare this common code and spit this out as a temporal representation.
A common problem between the two theories
These theories offer a simple and elegant explanation of the perceived unity of time. However, given the fragmented structure of the underlying timekeeping mechanism, that I discussed at the start and in the previous post, these kinds of theories might not cut. Sure they explain the perceived temporal unity of time, but they seem to do it at the cost of being unable to account for the empirical data that our timekeeping mechanisms that make time perception possible are fragmented in various ways.
The two theories both take time perception to make up a single unified psychological kind. But, from the perspective of the information processing that gives rise to our time perception, this just seems plainly false. The mechanisms underlying time perception are fragmented, and not a single unified mechanism.
In fact, I think that we should expect that it will be impossible to give one neat, unified story about how this fragmentation of timekeeping mechanisms is translated into a unified representational timeline that can underpin the perceived unity of time that we experience.