Music can be listened to during many everyday activities. North, Hargreaves, and Hargreaves [1] documented that roughly half of participants’ musical experiences occurred within the home, although approximately 18% of musical experiences occurred in public spaces. Some people listen to music all the time while walking, biking, or driving. In these situations, people should link visual exploration of outdoor scenes with processing of auditory stimuli (i.e., music). Wearing large studio headphones or earbuds that effectively silence all surrounding noise may create various dangerous situations. People need to be able to process information from the surrounding environment to avoid collisions with other people, cars, various objects, or simply for their orientation on a route. To date, there is insufficient knowledge of how this process works in real situations and to what extent the processing of acoustic information may restrict perception of visual information from the surrounding environment.

Heye and Lamont [2], in their study based on subjective reports of participants, propose that listeners create an “auditory bubble” while walking or travelling and listening to music and that they readily switch between inside (music) and outside (surrounding) worlds. In these listening situations, instead of perception of surrounding worlds, the attention might be directed to thoughts, memories, and emotions that are elicited by the music. Music turns people’s attention away from the environment toward inward experiences [3, 4, 5]. In this context, our previous study [6] investigated whether listening to music might mask effects of visual characteristics of a walking route at walking speed. Previous investigations revealed that people walking outdoors spontaneously react to various features of the surrounding environment, which results in a fluctuation of their actual walking speed [7, 8]. It was suggested that the absence of typical changes in walking speed at specific points on the route while listening to music reflects individuals not paying adequate attention to the environmental features of a location. The results revealed that music masked the influence of the surrounding environment only to some extent. Fluctuations in walking speed at specific locations on the route still appeared but were smaller compared to no-music conditions. Thus, the study demonstrated that visual exploration of the surrounding environment may be affected by simultaneously listening to music.

Gaining deeper insight into these processes will require more precise knowledge of how visual exploration of outdoor scenes may be influenced by the simultaneous processing of music. Clearly, analysis of eye movements can provide a better understanding of this problem because research in cognitive neuroscience shows that eye movements are closely linked to visual attention processes [9, 10, 11]. Although there are numerous studies of eye movements and various musical activities in the field of sight-reading research [e.g.,12, 13, 14, 15], analysis of eye movements in the perception of outdoor scenes while listening to music has started to be investigated only recently. To date, there have been only two relevant eye-tracking studies [16, 17]; however, they investigated different facets of this problem. Schäfer and Fachner [17] were interested in the attentional shift from visual perception of outdoor scenes to absorption in music, while Maróti and her colleagues [16] investigated changes in eye movement parameters (such as fixation duration, saccade duration, saccade amplitude, and saccade number) in relation to musical tempo.

The study by Schäfer and Fachner [17] provided new information on how eye movements can be influenced by participants simultaneously listening to music while observing outdoor scenes. They examined eye movements of participants viewing a picture (a house by the sea) or a film clip (a videotaped road trip on an empty road through an open landscape) while listening to familiar music, unknown music, or in silence. Popular music, with a tempo of approximately 120 beats per min (bpm), was used as the acoustic stimulus. The authors proposed that listening to music elicits an attentional shift from the outer to the inner world (provoked by absorption in music and the emotions and memories it evoked), resulting in lower eye activity. Their data indicated that music significantly reduces eye-movement activity, with participants exhibiting longer fixations, fewer saccades, and more blinks when they listened to music than when they sat in silence. As a possible explanation, they discussed either an attentional shift from the outer to the inner world or simply a shift of attention from visual to auditory input.

Studies investigating eye movements with different types of auditory stimuli show various results. Coutrot, Guyader, Ionescu, & Caplier [18] investigated the viewing of videos with and without their original soundtracks and found longer fixation durations and longer saccade amplitudes in an audio–visual condition than in a visual one. In the study by Maróti et al. [16], participants listened to drum sequences while viewing various natural scenes. It was found that fixation durations and average intersaccade intervals were longer for the drum sequence conditions compared with the quiet condition. On the contrary, Song, Pellerin, and Granjon [19] reported shorter fixation durations in an audio–visual (sounds, music) condition compared to a visual condition while observing video excerpts. The most recent study by Lange, Pieczykolan, Trukenbrod, and Huestegge [20] showed faster total reading time and faster reading completion time in the music compared silence condition. In contrast, some eye-tracking studies that investigated reading with presentation of auditory stimuli revealed no effect of background music. The study by Cauchard, Cane, and Weger [21] examined the influence of background speech and music on overall reading time (the summed fixation durations) using an eye-movement paradigm and found that background music had no effect on reading process or on eye movements while reading. Similarly, Johansson, Holmqvist, Mossberg, and Lindgren [22] found no significant differences between acoustic conditions (preferred or non-preferred music, noise from a café, silence) for the eye movement measures (fixation duration, saccadic amplitude) during reading.

In investigating eye movements while viewing outdoor scenes together with listening to music, we must take into account that recent research in environmental psychology has revealed that certain environmental features have different effects on eye-fixation behavior. Dupont, Antrop, and Van Eetvelde [23] investigated eye movements while viewing photographs of various landscape types in Belgium that differed in degree of openness and heterogeneity. They found a greater number of fixations in enclosed compared to open landscapes and a greater number of fixations in heterogeneous than in homogeneous landscapes. More importantly, eye-tracking studies by Berto, Massaccesi, and Pasini [24] and Valtchanov and Ellard [25] reported reduced eye-movement activity in terms of number of fixations and eye-travel distance while viewing photographs of natural scenes in contrast to urban scenes. Similar results were found in our recent study [26]. Although the mentioned studies were conducted in a laboratory, similar effects have been shown for viewing real natural environments and various forms of surrogate nature [27]. The difference between viewing natural and built scenes was explained in terms of better perceptual fluency while processing natural scenes compared to urban scenes [28]. Evidence is emerging that fractal complexity, typical of natural scenes, may be a source of perceptual fluency [29]. Fractals capture order and structure by the repetition of similar visual information across multiple scale levels. Thus, walking with music in an urban environment might require more attentional resources, not only because of the necessity to observe traffic and the movement of other pedestrians, both of which are more common in urban than natural environments, but also because a built environment is more difficult to visually process than a natural one [e.g., 30].

To sum, the previous studies [24, 25] found a higher visual exploration while observing urban scenes compared to natural scenes, which is manifested in shorter fixation durations, longer eye travel distance, and a higher number of fixations. It is suggested that processing of urban scenes requires greater visual exploration, compared to natural scenes, because they are more difficult to process. The investigations of processing outdoor scenes while listening to music [16, 17] observed significantly longer fixations while listening to music compared to the no-music condition, which suggests that listening to music while viewing visual images requires additional attentional resources. Thus, there is a question of how these two processes interact with each other, and whether the effect of background music on eye-movement behavior while viewing a scene in comparison to a silent control may be modulated by the type of scene (urban vs. natural).

A further question is whether music tempo might affect the motor system of gaze control. Our study was designed to explore the effect of fast-tempo music in contrast to slow-tempo music and a no-music condition on eye movements. There is a large body of research documenting how certain temporal properties of music (such as rhythm or tempo) induce motor processes in a listener [for review, 31, 32]. The tempo of music can influence the speed of movements in various behavioral domains. For instance, the tempo of music can influence walking speed [e.g., 6, 33, 34] and the speed of various sports activities [35, 36, 37, 38]. Studies from the field of consumer psychology suggest that the tempo of in-store music might influence visual exploration and the consequent process of consumer decision-making [e.g., 39, 40]. Music can also influence mood and arousal level before/during sports performance [41, 42, 43, 44], resulting in an improved performance. Karageorghis, Terry, and Lane [45] developed a conceptual framework for predicting the motivational qualities of music in exercise and sports environments. The authors argue that some types of music motivate bodily movements (namely, in sports), while others do not. To strengthen the effect of tempo, in selecting musical stimuli, we employed Karageorghis’s concept of motivational and non-motivational music [45]. Both types of music were used in our previous study [6], in which participants were asked to walk with music along an urban route. The study showed that fast motivational music accelerated walking speed, whereas slow music decreased walking speed, in contrast to common popular music of diverse tempi.

Because eye-movement behavior is inherently rhythmic, an important question is the possible synchronization between eye movements and a musical beat, which may also have some implications for visual processing of perceived scenes. This line of research is based on the Dynamic Attending Theory [46]. According to this theory, the brain works on the basis of internal neural oscillations that are capable of entraining to external events and targeting attentional energy to expected points in time. In accordance with this theory, it can be expected that if visual attention synchronizes to the rhythm of musical beats, the rhythm of eye movements would align with the musical beats as well [16]. Maróti and her colleagues [16] investigated the effects of music tempo (drum grooves) on the eye movements of participants viewing various natural scenes. They used drum grooves with either 102 or 144 bpm. The results revealed that slow musical beats retarded sampling of visual information. Fixation durations significantly increased at the lower beat frequency compared to the higher beat frequency and to the no-music condition. Although the study revealed modulation of eye movements by a musical beat, it did not find evidence for entrainment. Consistent with Maróti et al.’s [16] findings, Lange et al. [20] used basic musical stimuli (bass drum, synthesized sequence of chords) and reported that increased tempo of the musical stimuli (80–140 bpm) accelerated eye fixations during text reading (but did not affect a visual scanning task). However, the most recent study by Plöchl and Obleser [47] provides contradictory findings. Their participants viewed either a blank gray screen or a scene from a picture book while listening to either isochronous or irregular auditory clicks at different temporal frequencies between 180 and 300 bpm. Auditory stimulation, however, had no significant impact on saccade frequency or timing, either under rhythmic or arrhythmic conditions. Although these mentioned studies used different visual stimuli and auditory stimuli of different tempi and complexity, it can be concluded that the effect of speed of auditory beats on the gaze control motor system needs further clarification.

The aim of the present study was to investigate eye movements while viewing urban or natural scenes while listening to two different types of music, namely fast music that motivates bodily movements and slow music. In view of the above literature, we expect that listening to music while viewing outdoor scenes will increase fixation durations compared to observing the scenes without music. Further, the effect of the environmental features of the observed scene and the interaction between the type of scene and music condition will be examined. We expect fixation durations will decrease while viewing urban vs. natural scenes. This should be the case, because of a lower perceptual fluency of urban scenes compared to natural scenes. We also expect that fixation durations will increase when music is presented. Finally, there is a question of whether music tempo will modulate the speed of eye movements. We predict that increased musical tempo will decrease the duration of fixations.

This study analyzed eye movements while viewing urban or natural scenes while listening to two different types of music – fast music that motivates bodily movements or slow, non-motivational music – or silence. Significantly shorter fixations were found for viewing urban scenes compared with natural scenes, but we did not find a significant interaction between the type of scene and music condition. The results revealed shorter fixation durations on the range of 30 ms in the no-music condition compared to both music conditions, but these differences were not significant. Moreover, we did not find differences in eye movements between music conditions with either a fast or slow tempo.

While previous studies [16, 17] observed significantly longer fixations while listening to music compared to the no-music condition, which suggests that listening to music while viewing visual images requires attentional resources, we did not succeed in fully replicating these results. Although we did not find significant differences between the music and the no-music condition, we observed a similar trend in both fixation durations and the number of fixations for both the entire viewing time and during the temporal evolution that is consistent with the previous studies [16, 17].

It should be mentioned that the 60Hz sampling rate of our apparatus may be one limitation of this study. While many significant effects on fixation durations are in the range of 30 ms (e.g.,16-19], we did not find significant differences between no music and musical conditions occurring in this range. One possible explanation is that the lower sampling rate of our device might cause higher variability in the data. However, there are also other additional possible explanations.

Schäfer and Fachner [17] used two types of music: self-selected music with the predicted effect of absorption and music from the experimenters, for which absorption was not predicted. However, listening to background music does not necessarily mean that listeners are fully engaged in music listening while performing other activities. Some studies conducted in a service environment (restaurants, shops) showed that people are not often aware of the presence of background music [e.g., 49], particularly if they like the type of music being played. Clearly, listening to background music while viewing scenes does not necessarily recruit a considerable amount of attentional resources to have a conspicuous effect on eye movements. An interest and engagement in the music being played may be an important factor. In Schäfer and Fachner’s [17] study, the participants were asked in advance to bring their favorite music, which may, in general, attract their attention to music in the course of the experiment because they simply may suspect that the experiment has something to do with music perception. Similarly, in Maróti et al.’s [16] study, participants had to perform a tempo discrimination task that may also draw attention to drum sequences during viewing outdoor scenes. In contrast, the experimental procedure used in our study did not necessarily imply that music would be an important part of the experiment.

It should be noted that individual variables might also have an effect on the influence of music on eye-tracking behavior. Although people have individual musical preferences depending on diverse factors [e.g., personality, see 50], we do not expect a confounding effect of musical preference because the musical excerpts used in the experiment were examples of easy-listening popular music. However, individual differences in everyday use of music might potentially have some influence. Chamorro‐Premuzic and Furnham [51] noted that there are three different major uses of music. For some people, music serves mainly for emotional regulation and mood manipulation. Other individuals are characterized by a cognitive approach, which means rational or intellectual processing of music. Finally, background use of music is typical for people who use music as a background for social events, work, or interpersonal interaction. There are also links between these diverse types of music uses and certain personality traits, as found in Chamorro‐Premuzic and Furnham [51]. Clearly, further research should also control for the potential effect of these differences.

Another considerable factor is participants’ musical experience, which may affect their interest in musical or acoustic stimuli while viewing scenes. There is evidence that musicians perceive auditory differences more finely than non-musicians and that they are slightly better at sustained auditory attention than non-musicians [e.g., 52]. Musicians are also better than non-musicians at pre-attentively extracting information out of musically relevant stimuli [53]. Our participants had no formal musical training, and therefore it is unlikely that musical expertise played a confounding role in our study. However, it is worth noting that Schäfer and Fachner’s [17] study did not describe their participants’ musical expertise. In Maróti et al.’s [16] study, some participants were musicians, but the authors did not find any effect of music training. On the other hand, the participants in this experiment listened to simple musical structures, namely, drum sequences. A future research should consider musical expertise as a factor that may play some role.

Although it is usually stated that the average fixation duration for scene perception is between 260 and 330 milliseconds [e.g., 54], the fixation durations found in our experiment were longer. However, it is known that fixation durations for scene perception vary as a function of the task and the characteristics of the scene. For instance, fixation duration is longer for full color photographs than for black-and-white line drawings [55]. They may also be affected by scene luminance [56] and contrast [57]. For instance, in Schäfer and Fachner’s [17] study, average fixation duration values in the no-music condition ranged from 340 to 391 msec.

It is also worth commenting that the duration of visual stimulus presentation might also affect the findings because there might be differences in eye-movement activity between early and late phases within the trial. While in Maróti et al.’s [16] study the participants watched the image for 6 s, in Schäfer and Fachner’s [17] study it was for 45 s, and in our study it was 15 s. However, our analysis of temporal evolution of eye-movement measures within the trial did not reveal significant changes in relation to music condition, though there was an effect of increased fixation duration over image time on screen. It shows that duration of stimulus presentation may also affect the results.

One further question was whether the effect of background music on eye-movement behavior during scene viewing, in comparison to a silent control, may be modulated by the type of scene (urban vs. natural). In accord with previous studies [24, 25, 26], the results showed significantly shorter fixations for viewing urban scenes compared with natural scenes, which is explained in terms of a higher perceptual fluency of natural scenes with respect to ordinary urban scenes. However, our analysis did not reveal any interaction between music and type of scene. This shows that music processing does not interfere with scene processing.

The final question was whether music tempo would modulate the speed of eye-movements. In our study, we did not find differences between the effects of fast and slow music on eye movement. This finding is in contrast with Maróti et al. [16], who reported that the beat frequency of the drum grooves modulated the rate of eye movements, specifically fixation durations, which increased at a lower beat frequency rather than at a higher beat frequency. As we already mentioned, a limitation of our study is that the sampling rate of the eye tracker used did not enable us to measure small differences of approximately 10 ms precisely, as would be expected for beat entrainment. Moreover, it is suggested that the effect of beat frequency on eye movements may be also influenced by the type of musical stimuli and the experimental procedure. In Maróti et al.’s [16] study, the participants listened to the isolated sound of drums; drum grooves might strengthen beat perception. Our stimuli involved ordinary music without a stressed beat. On the other hand, harmonic structure of the pop songs used in our experiment may reinforce metric structure and therefore a beat may be more easily perceived.

However, an alternative explanation is also possible. While Maróti et al. [16] had used music of 102 and 144 bpm to make the effect of musical tempo on eye movements more distinctive, we used tempi with a more salient difference in our experiment. It might be possible that with such a very fast tempo at 187 bpm, participants might extract spontaneously the beat at half of the speed of the music, that is 93 bpm. Moreover, there is a short half time section in the song “One Fine Day”, which can reinforce the 93 bmp feel. If so, the difference between slow music at 69 bpm and fast music with 93 bpm would not be so strong. Interestingly, in our previous experiment [6], in which we explored synchronization between music tempo and walking speed, we found that only one participant synchronized her steps with the beat of the music while listening to a musical piece at a tempo of 187 bmp. Curiously, to synchronize, instead of walking, she was running. However, we did not control bodily synchronization with music in this experiment or the beat extraction process. Clearly, further research should specify the circumstances in which the musical beat may affect eye-movement velocity.

To conclude, the effect of music on eye movements while freely observing outdoor scenes is still not entirely clear. We suggest that the type of stimuli, the specific experimental procedure, and the interest and engagement of participants in listening to background music while processing visual information are important factors that influence attentional processes and the attentional shift from visual to acoustic input, which is manifested in eye-movement behavior.