Motor Synchronization in Patients With Schizophrenia: Preserved Time Representation With Abnormalities in Predictive Timing

Abstract

Objective: Basic temporal dysfunctions have been described in patients with schizophrenia, which may impact their ability to connect and synchronize with the outer world. The present study was conducted with the aim to distinguish between interval timing and synchronization difficulties and more generally the spatial-temporal organization disturbances for voluntary actions. A new sensorimotor synchronization task was developed to test these abilities. Method: Twenty-four chronic schizophrenia patients matched with 27 controls performed a spatial-tapping task in which finger taps were to be produced in synchrony with a regular metronome to six visual targets presented around a virtual circle on a tactile screen. Isochronous (time intervals of 500 ms) and non-isochronous auditory sequences (alternated time intervals of 300/600 ms) were presented. The capacity to produce time intervals accurately versus the ability to synchronize own actions (tap) with external events (tone) were measured. Results: Patients with schizophrenia were able to produce the tapping patterns of both isochronous and non-isochronous auditory sequences as accurately as controls producing inter-response intervals close to the expected interval of 500 and 900 ms, respectively. However, the synchronization performances revealed significantly more positive asynchrony means (but similar variances) in the patient group than in the control group for both types of auditory sequences. Conclusion: The patterns of results suggest that patients with schizophrenia are able to perceive and produce both simple and complex sequences of time intervals but are impaired in the ability to synchronize their actions with external events. These findings suggest a specific deficit in predictive timing, which may be at the core of early symptoms previously described in schizophrenia.

Keywords: predictive timing; schizophrenia; sensorimotor synchronization; tapping; timing and time perception.

FIGURE 1

Experimental protocol. (Left) The left panel illustrates a top view of the tactile screen on which the picture of the targets was displayed throughout each trial. The visual targets consisted in six equidistant circles (diameter: 1.2°) arranged in the form of a hexagon. (Right) The right panel is a picture of a participant who was asked to point clockwise each circle, one after the other, in synchrony with a series of beeps (N = 30 or 34 depending on auditory sequences). These sounds were emitted by a computer and played through table-top speakers.

FIGURE 2

Schematic illustration of the auditory sequences and measured variables (IRI and ASYNC), which were used as indicators of the performance levels observed in the sensorimotor synchronization task. Participants were instructed to synchronize their finger-tap following two different auditory sequences. Isochronous sequences were constituted of equivalent inter-stimulus intervals (ISIs) of time (Top: R-eq; ISI = 500 ms). Non-isochronous sequences were composed of alternating time intervals (Bottom: R-alt; ISI = 300/600 ms or ISI = 600/300 ms). This figure also specifies the indicators used to characterize the participants’ timing performances. The inter-response interval (IRI) refers to the time interval between the onsets of two successive taps produced by a participant (Top) and reflects the participants’ ability to produce accurately a timed motor sequence. The asynchrony indicator (ASYNC) was calculated as the time interval between the first detected point of contact between the finger and the screen (i.e., the tap action) and the start of the nearest tone. It is a marker of the participants’ ability to produce a motor response in synchrony with a predictable external event. By convention, signed asynchronies are negative when the tap is ahead of the target beep (e.g., ASYNC 1), and positive when the tap lags behind (e.g., ASYNC 3). ISI, inter-stimulus interval; IRI, inter-response interval; ASYNC, asynchrony (in ms)

FIGURE 3

Mean inter-response intervals (IRIs in ms – with their respective standard errors) in the equivalent isochronous rhythmic condition (Left: R-eq) and in the alternating non-isochronous rhythmic condition (Right: R-alt) as a function of the group (controls; patients). For the R-alt trials, the overall tempo combines results obtained for the long intervals (600 ms – coded with hatched lines) and for the short intervals (300 ms – coded with full color).

FIGURE 4

Mean signed asynchronies (ASYNC in ms) (with their respective standard errors) in the equivalent isochronous rhythmic condition (Left: R-eq) as a function of the group (controls; patients). On the (Right), the time series of these results are presented for the total of 34 taps in controls (black dots) and in the patients (gray dots). The black vertical line illustrates the boundary from which the first six taps of each trial was discarded for the analyses. Indeed, it took a few beats for the participants to get into the pace set by the metronome.

FIGURE 5

Mean signed asynchronies (ASYNC in ms) (with their respective standard errors) in the alternating non-isochronous rhythmic condition (Left: R-alt) as a function of the group (controls versus patients). On the (Right), the time series of these results are presented for the total of 30 taps in controls (black dots) and in the patients (gray dots). The black vertical line illustrates the boundary from which the first six taps of each trial was discarded for the analyses. Indeed, it took a few beats for the participants to get into the pace set by the metronome.