Migraine is a common, disabling disorder that is highly prevalent in the general population [
1,
2]. Migraine without aura, which has no early unusual symptoms, is the most common form of migraine. Photophobia and phonophobia are the most prominent symptoms for patients with migraine without aura [
3,
4]. The intensities of photophobia and phonophobia correlate positively with the intensity of headache pain [
5,
6]. These findings demonstrate that the intensity of one migraine symptom is associated with the intensity of other migraine symptoms. Moreover, hypersensitivity to a unimodal stimulus may not be restricted to that stimulus, but it may also lead to the further elevation of hypersensitivities to other stimuli; for example, the exposure to light can lead to greater hypersensitivity to sound [
7]. Therefore, it is inadequate to independently research only one migraine symptom. In daily life, most external information is received from vision and sound signals. Vision and sound signals are received separately and integrated in the human brain and, thus, provide a comprehensive understanding of the real world. Therefore, it is important to study integration across sensory modalities. Recently, Schwedt [
7] illustrated the significance of interactions between the processing of signals for understanding migraine symptoms and their underlying mechanisms.
In healthy subjects, some studies that investigated cross-modal processing regarding vision and sound have shown that bimodal audiovisual stimuli can be discriminated or detected more accurately and faster compared with unimodal auditory or visual stimuli presented alone [
8,
9]. This facilitative effect is called “audiovisual integration”. Conversely, audiovisual suppression reflects the response to audiovisual stimuli that produce a significant decrease in the neuron’s activity as compared with the responses to unimodal stimuli [
10]. Many studies of audiovisual interaction have investigated healthy subjects when visual and auditory stimuli were simultaneously presented [
8,
11,
12]. However, the multisensory information may be temporally asynchronous in real life; for example, we first see lightning and then hear thunder. To adapt to the environment, the brain can integrate audiovisual information over a wide range of temporal gaps and correctly match auditory and visual signals [
13,
14]. In some neurons, combinations of auditory and visual stimuli delivered at specific intervals (50 and 150 ms) can produce greater responses. However, at longer intervals (200 and 300 ms), audiovisual stimulation either produces a reduction of a neuron’s response or no interaction [
10]. Moreover, Talsma et al. [
15] found that the processing of auditory and visual stimuli across specific temporal intervals was influenced by attention in a visual and auditory discrimination task using event-related potential (ERP). Their results showed that the attention effects on the right-hemisphere visual P1 were largest in the visual with auditory delayed by 50 ms condition. However, some studies found that attention to the unimodal visual or auditory signal is different in patients with migraine with normal controls. For the unimodal visual stimulus, migraineurs have a wider reactive field of activation compared with normal controls because of the sensitivity of the occipital cortex to light stimuli [
16,
17]. Furthermore, the heightened excitability of the visual cortex affects the top-down attentional control of the visual cortex in a visual spatial attention task [
18]. For the unimodal auditory stimulus, Demarquay et al. [
19] investigated migraineurs with a classic auditory habituation paradigm. Their results showed that the auditory orienting component (N1) was larger in migraineurs compared with normal controls, which suggests that automatic attention is increased in migraineurs. These findings suggested that attention is greater in patients with migraine compared with normal controls as a result of the hypersensitivity of migraineurs to an auditory or visual stimulus. Furthermore, some researchers have reported that attention could modulate audiovisual interaction processes, and that audiovisual integration was larger in the attended conditions compared with the unattented conditions [
20]. Thus, in the conditions with attending visual and auditory signals, we predicted that the audiovisual integration elicited by audio-visual stimuli across temporal intervals in patients with migraine without aura would be greater or have a wider range of temporal gaps compared with normal controls.
To confirm our predictions, we designed a visual and auditory discrimination task that used conditions with attending visual and auditory signals. The stimuli contained visual, auditory and audio-visual stimuli across different temporal intervals, which were randomly presented with equal probability. Each stimulus type contained a standard and a target stimulus. The task of the subjects was to respond to the target stimuli. By comparing the audiovisual integration between the patients with migraine without aura and the normal controls, we examined whether the audiovisual temporal interaction of the patients with migraine without aura would be greater and have a wider range of temporal gaps compared with the normal controls.