Last time we discussed how the experienced time of events relates to both the real time of events and the time of neural processes underlying the experiences.
The brain-time view proposes one very popular (among psychologists) way to cash out this relation. The brain-time view states that the order of events represented in our experience is determined by the time at which neural processes reach their perceptual endpoint.
The perceptual endpoint refers to the moment at which some stimulus has been processed by some specialised sensory transduction mechanism. Thus, for example, if a stimulus reaches a perceptual end point before another stimulus reaches its end point the two are experienced to occur in this order.
The philosopher Valtteri Arstila (2015, 2016) defends this view and furnishes it with three principles, two of which we discuss here.
The thesis of minimal delay: Our experiences are only ever delayed by the time it takes for the stimulus to reach us and for our neural mechanism to process it.
The thesis of temporal isomorphism: The subjective time of experience is determined by the time of the neural process realising the experience.
These two principles make up a very simple view of the mechanisms responsible for temporal experiences. The experience of time comes for free when our neural mechanisms process stimuli in our environment.
However, neither of these principles come without their issues. Starting with ‘The thesis of minimal delay’ we see how delays can quickly add up. Although neural mechanisms are fast, every bit of processing adds a delay to the time of experience. This means that we would always be ‘living’ slightly in the past due to neural latencies.
Both latencies differ within and across different sensory modalities and the different mechanisms have little or no information about these various latencies. Such a system would make deducing the actual time of external events practically impossible, which you could imagine could have grave consequences if we are ever in a situation where getting the timing right means life or death (or something less dramatic).
The other problem concerns ‘The principle of temporal isomorphism’. When you first read it, the principle sounds almost trivially true. “We experience an event to take place at the moment that we enjoy the experience of that event”. Yet in saying this we make a few assumptions.
Firstly, the principle assumes that there is a determinate fact about when experiences become conscious. Secondly, it assumes that the time at which a neural process takes place cannot come apart from the time that neural process represents - that temporal information is implicit in the processing itself.
I think both these assumptions are false. Let us take a look at the second assumption as the first one is a bit harder to unpack.
The second premise states that to experience a flash and a sound occurring in sequence, the neural processing of the flash must be finished before processing the sound. But is this right?
Consider the non-neural case of hearing the sentence “Tom arrived after Bill did”. In this case, the temporal content of the sentence states that Bill arrived then Tom arrived, but in the sentence representing this temporal content you learn about Tom’s arrival before Bill’s. This is a very simple way in which the representation of temporal content and the temporal content represented come apart.
Returning to the neural case, there are numerous examples from psychology where the timing of neural mechanisms depart from the temporal relations represented in experience (Vroomen et al. 2004; Cai, Stetson & Eagleman 2011; Roseboom & Arnold 2011).
In one kind of experiment, participants are continuously presented with the same asynchrony between a sound and a flash (235ms). After having seen this sequence of flashes and sounds over three minutes, participants started to perceive the sound and flash to occur closer together than the first time they saw it. This compensation for the asynchrony between two stimuli shows up in multiple modality pairings (Di Luca et al. 2009) and for delays between self-instigated action and their sensory effect (Stetson et al. 2006).
What is particularly damming for brain-time views is that these compensations do not seem to be caused by changes in the time when neural mechanisms process the stimuli. Cases like this prove difficult cases to explain if one accepts the second assumption of the principle of temporal isomorphism, we should not expect any such compensation to occur.
What about the first assumption of the principle of temporal isomorphism? ‘that there is a determinate fact about when experiences become conscious’. This is harder to disprove empirically. It is more likely that there are conceptual reasons for thinking that this assumption is false.
Why think that there is some definite moment an experience becomes conscious? Well because we seem to be conscious at every waking moment. It seems intuitively reasonable to assume that there is a time when we are conscious of one thing and another time when we are conscious of another.
But how can it be that all our conscious experience at every waking second seems fully coherent and complete if they become conscious whenever the neural mechanism is processed?
In the last post, we mentioned how our different sensory mechanisms responsible for processing sensory features are widely distributed over multiple areas of the brain. The sensory processing of these mechanisms also takes place at different times and takes different amounts of time to fulfil their functions. Moreover, these systems do not have direct access to each other, so they cannot share information to collectively create a coherent representation of the external world. If the principle of temporal isomorphism is true, it would seem like magic if this temporal puzzle just arranges itself into neat coherent representations as if it was the result of pre-established harmony.
To save the principle one could be attempted to think all the information of these sensory mechanisms stream together somewhere where they are collectively processed and made conscious. In this way, we postpone the perceptual endpoint a bit so that representations can line up with each other. One could then say that they become conscious the moment they come together and are processed in this special place. If this story was true, then it would be true that there is a definite moment when some experience becomes conscious.
But there probably is no such place in the brain where sensory information goes to enter conscious experience. It would also be biologically implausible that the brain should make use of a central integration system like this, and subjectively impossible to determine whether there is any such thing as a determinate moment where we enjoy experiences.
At any moment we are aware of a lot of different things, at least we seem to be so when we are asked about happenings in our environment. But whether we make up our minds when we are asked about what we are currently experiencing or whether we were aware of it at the moment is impossible to determine first-personally or third-personally.
There might not be anything like a definite moment experience, but rather a large number of representations resulting in a continuous flow of experiences that are constantly fading in and out of each other in experience with no determinate start or end point. Which temporal experiences we enjoy might then be determined by the temporal context we are in, the time-sensitive behaviour we are engaged in, and the temporal content of representation available to the system, rather than our temporal experience being determined by when certain neural mechanisms are done representing a stimulus.
Although these issues might be answerable by the defender of the brain time view, we see that its intuitive and simple explanation comes with its problem that requires quite convoluted answers. And so goes the simplicity…