“An hour, once it lodges in the queer element of the human spirit, may be stretched to fifty or a hundred times its clock length; on the other hand, an hour may be accurately represented by the timepiece of the mind by one second. This extraordinary discrepancy between time on the clock and time in the mind is less known than it should be, and deserves fuller investigation.”Virginia Woolf, Orlando
As Woolf nicely puts it, there is a discrepancy between time in the mind and time on the clock. In other words, subjective time does not equate to objective time. Although we all agree on what time it is or how many hours have passed since sunrise if we checked the clock, experience of time reflects individual and situational differences. It has been very well established that the internal state of the observer modulates time perception. For example; attention, emotional state, and task demands affect how we perceive time. Time flies when we are bursting with happiness, but it stands still when we are facing a dangerous condition. Some people even report that time stops or ceases to exist during meditation. Of course, the wristwatch tells something different. Consequently, clock time must be distinguished from time perception, which could be defined as a concept that describes the subjective experience of time and how a person interprets the duration of an event.
We all experience time subjectively, it is crystal clear. But, have you ever heard that certain groups of people demonstrate significantly different patterns in time perception compared to the rest of the population? Further, could you imagine that time perception could be distorted or somehow be related to the psychopathology of a mental illness? Yes, indeed! Schizophrenia patients display timing abnormalities, which is assumed to be a key process in schizophrenia pathogenesis. Considering the importance of time-related judgements in our daily lives, studying time perception dysfunctions in schizophrenia patients may shed light on difficulties experienced by these patients. Hopefully, grasping the role of timing abnormalities in the development of symptoms may contribute to the understanding of the disease itself. Before delving into the literature of time perception in schizophrenia from a neuroscientific perspective, it is very useful to go through the mechanisms of time perception in the mind and brain first.
Models of time perception
Time perception over fine scales (e.g., milliseconds) is critical for maintaining our lives, organizing speech recognition and production, motor coordination or sound localization among many other functions. Although multisensory information is received by sensory receptors over time, there is no specialized receptor for the transduction of time. Still, time perception is framed by the anatomical and dynamical constraints of the nervous system. However, the brain is in a pretty pickle! Signals from different modalities are processed at different speeds in the brain and these signals must get aligned to correctly represent the outside world. For example; in the visual system, motor and color pathways are processed with different latencies; but we are able to perceive a temporally unified ‘moving green ball’. These temporal processes escape from our consciousness, that’s why they are called ‘implicit timing’.
On the other hand, conscious awareness of the passage of time and estimation of durations involve an explicit representation of time, as occurs in interval timing, which is scaled in seconds or minutes. Interval timing requires attention, working memory and decision making ability, which are categorized as ‘higher-level cognitive functions’. Because most of the studies on time perception focus on interval timing, several models have been developed to describe the mechanism behind it. The most prevailing model, which is called the pacemaker-accumulator model, assumes the existence of a central clock. According to the model, a pacemaker or oscillator sends pulses which are accumulated in a counter(working memory). The number of pulses counted basically determines the duration of an interval. Contrastingly, recent models hold the view that no central clock is present. For example, thestate-dependent network model claims that time perception depends on time-dependent changes in the state of the neural networks instead of a clock-like internal mechanism. To put it simply, durations are represented as spatial patterns of activity and estimating durations requires recognizing these patterns.
A neuroscientific approach towards time perception
After reading the paragraphs above, you might wonder how these mechanisms of time perception relate to the brain regions. Over the past 15 years, it has been consistently found that specific structures in the human brain are contributing to the processing of temporal information. Diverse brain regions including dorsolateral frontal cortex, basal ganglia,insula, parietal cortex, cerebellum and hippocampus are associated with time perception. Despite time perception in millisecond range is mostly restricted to processes in subcortical structures of the brain, time perception in seconds to minutes range is reflected in the thalamo-cortico-striatal circuit.
Isn’t it difficult to understand what really happens in a brain region or in a circuitry without a model? Luckily, we have the Striatal Beat Frequency Model, which attributes timing to a distributed neural activity in the brain. According to this model, the striatum receives numerous impulses from the cortical neurons when a ‘start signal’ is given. The neurons’ firing synchronizes and they create specific patterns of activity. The substantia nigra sends a signal to the striatum when time-keeping activity needs to finish. Here, the striatum takes a computational role! The pattern of activation is finally recorded by the burst of dopamine, identifying an interval length. The role of dopamine is critical to time perception, shown in the fact that psychoactive substances like cocaine and amphetamine alter time perception via accelerating the speed of the internal clock.
Distortion of time perception in schizophrenia
We have just reviewed the mechanisms of time perception in the brain, so that distortion of timing could make more sense now! Although there is not any clinical condition that could be categorized as a disorder of time perception, several patient groups show distortions in varying degrees, for example in Parkinson’s disease, ADHD, autism and schizophrenia. Especially, time perception distortions in schizophrenia is an increasingly known phenomenon, which dates back to the beginning of the last century.
For example, Scott and Clifford (1948) reported that some patients usually get confused about time. A schizophrenic patient claimed that he looked at the clock and looked again an hour later and it was the same time. Sure, hearing sentences as such may not be surprising because we use them as a metaphor a lot. However, considering that one literally says it because of a distortion in time perception is actually very perplexing! Time perception dysfunction is not the only characteristic of schizophrenia. Rather, it is an acquired psychiatric disorder which is defined by following three categories of symptoms: positive (e.g., hallucinations or delusions), negative (e.g., lack of emotional reactivity), and disorganized symptoms (e.g., rambling speech).
What happens when schizophrenic patients perform timing tasks? A study by Carrol et al. (2008) employed a temporal bisection task, in which participants are first trained to discriminate between two reference durations (long and short) and then asked to categorize intermediate durations based on their similarity to previously studied reference durations. Schizophrenia patients, the majority of whom were on antipsychotic medications, showed the ‘modality effect’ described by that visual signals are judged to be shorter than auditory signals with the same duration, like control group. Although there was no difference between two groups in visual modality, schizophrenia patients displayed greater auditory timing variability which implies less temporal precision.
In addition to the temporal bisection task, estimation and production tasks were also employed by researchers who are interested in time perception in schizophrenia. In the estimation task, participants were requested to simply estimate how much time passed; whereas in the production tasks, they are asked to wait for producing the duration passed. Numerous studies, which used estimation and production tasks, demonstrated that time perception in schizophrenia is highly variable. Interestingly, different studies draw inconsistent conclusions. The patients overestimate or underestimate the duration in estimation tasks, while they overproduce or underproduce in production tasks compared to controls. Thus, more recent studies define time distortion as variable, instead of supporting a specific direction.
But, how are the differences between patient and control group represented in the brain? An fMRI study by Davalos et al. (2011) found that differential patterns of brain activation were observed for schizophrenic and control groups as a function of task difficulty. Again, the temporal bisection task which applies 200 ms as a reference duration was used.In the easy condition, participants were asked to judge durations between 70 and 300 ms; while in the difficult condition, the range was 160-240 ms. In both conditions, the patient group made more errors compared to the control group. Also, supplementary motor area, insula and striatum, which are associated with time perception were found to be less active in the schizophrenic group. Lastly, the difference between patient and control group increased in difficult condition.
Time perception relates to positive symptoms
Positive symptoms of schizophrenia such as hallucinations or delusions create unbearable difficulties for the patients. Recently, abnormalities in time perception have been assumed to contribute to the generation of positive symptoms. For instance, it was found that auditory hallucinations correlate with disturbances in timing. Importantly, a meta-analysis study in 2018 showed that there is a link between positive symptoms of schizophrenia and accelerated time perception. But how?
It was suggested that abnormal coordination between frontal and posterior brain regions brings about distortions in temporal organization of sensory and motor information, which is essential for normal perception and behaviour. This is also consistent with the idea that schizophrenia is implemented by both the dysfunction of multiple cortical areas and their abnormal connection. In addition, positive symptoms are further explained by the impairment in the forward model, which is basically an internal control system required for estimating the sensory consequences of motor actions. When the sensorimotor prediction is erroneous, one might perceive that one’s own mental experiences are coming from outside. Time perception plays a critical role in forward model, explaining the link between positive symptoms and time perception abnormalities further.
Why is time perception distorted in schizophrenia?
As in many other disorders associated with dopaminergic dysfunction such as ADHD or Parkinson’s disease, abnormal dopamine activity (DA) in the frontostriatal network is present in schizophrenia. If you remember the Striatal Beat Frequency Model, it will strike you that dopamine is critical for time perception. Because the speed of the pacemaker in the counter model is modulated by DA, abnormal activity leads to highly variable time perception in schizophrenia. For example, if the speed of the pacemaker accelerated by DA, then the patient underproduces the interval length. In addition, schizophrenic patients have morphological abnormalities in the brain, matching with their cognitive dysfunctions. Many of the neuroanatomical changes due to the disease influence areas which participate in interval timing networks.
Lastly, some argue that impairment in higher cognitive processes such as memory and attention might interfere with various levels of time perception. For instance, impaired memory in schizophrenic patients results in crushing or stretching time intervals, causing inconsistent results in the literature. Recent studies also supported the role of working memory in time perception, suggesting an overlapping structures for these two processes.
Big Ben is wrong
It is now quite clear that distorted time perception in schizophrenia is present, along with its’ contribution to the psychopathology of the disorder. Since time perception is essential for many aspects of daily functioning, its’ role in the development of symptoms in schizophrenia should not be ignored. Also, looking at schizophrenia through timing abnormalities might open up unprecedented ways of understanding and treatment of the disorder. Further, studying with patient groups having timing abnormalities might help to improve the scientific literature on time perception. Virginia Woolf was heavily preoccupied with discrepancy between subjective time and time on the clock. She included Big Ben as an embodiment of clock time in almost every work to remind us that how we are deeply influenced by this discrepancy. And she was right…