Sounds App
Danita Roemer
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During the baseline period, the participants were asked to relax in silence. At the end of the period a prerecorded female voice reminded them that the first stress test was about to begin. After the stress test, the female voice instructed the participants to relax and one of the four experimental sounds was presented. This switch between stress test and recovery was repeated three more times (see Figure 1).
where y is baseline corrected SCL, x is time (in seconds) and b1, b2 and b3 are constants. Figure 4 shows the fitted functions for the four experimental sounds. The fit, R2, for the nature sound, low noise and ambient noise was > 0.99, it was slightly lower for the high noise, R2 = 0.96. RMS-error for the nature, high noise, ambient and low noise sound was 0.0088, 0.017, 0.0090 and 0.0097 μS, respectively. The half life recovery was calculated using Equation 1, by solving for x at the point where SCL had been reduced by half, compared with its value at x = 0 (see dotted line in Figure 4). The high noise had the longest half life of 159.8 s, the half life of the other three were 121.3 s for ambient noise, low noise 111.4 s and nature sound 101.3 s. Reliable statistical testing of individual half life values was not possible, since the estimated constants in several cases generated complex numbers, that resulted in missing data when half life values were calculated.
Skin conductance level (SCL) as a function of time, shown separately for the four sounds. Curves were fitted to the group data. Constants of Equation 1 and half life value (x) are indicated in each diagram.
The present results suggest that recovery from sympathetic arousal is affected by type of sound (nature sound versus noise). Recovery was faster during the nature sound (50 dBA) compared with the noises, including the low noise (50 dBA) and the ambient noise (40 dBA). The mechanisms behind the faster recovery could be related to positive emotions (pleasantness), evoked by the nature sound as suggested by previous research using non audio film stimuli [9]. Other perceptual attributes may also influence recovery. The Ambient noise was perceived as less familiar than the other sounds (Figure 2), presumably because it contained no identifiable sources. One may speculate that this lack of information might have caused an increased mental activity and thereby an increased SCL, compared with the nature sound (cf. [28]). An effect of sound pressure level can be seen in the difference between high and low noise, this difference is in line with previous psychoacoustic research [12] and is not a surprising considering the large difference (30 dBA) in sound pressure level.
Stressed plants show altered phenotypes, including changes in color, smell, and shape. Yet, airborne sounds emitted by stressed plants have not been investigated before. Here we show that stressed plants emit airborne sounds that can be recorded from a distance and classified. We recorded ultrasonic sounds emitted by tomato and tobacco plants inside an acoustic chamber, and in a greenhouse, while monitoring the plant's physiological parameters. We developed machine learning models that succeeded in identifying the condition of the plants, including dehydration level and injury, based solely on the emitted sounds. These informative sounds may also be detectable by other organisms. This work opens avenues for understanding plants and their interactions with the environment and may have significant impact on agriculture.
Attention restoration theory (ART) posits that stimuli found in nature may restore directed attention functioning by reducing demands on the endogenous attention system. In the present experiment, we assessed whether nature-related cognitive benefits extended to auditory presentations of nature, a topic that has been understudied. To assess directed attention, we created a composite measure consisting of a backward digit span task and a dual n-back task. Participants completed these cognitive measures and an affective questionnaire before and after listening to and aesthetically judging either natural or urban soundscapes (between-participants). Relative to participants who were exposed to urban soundscapes, we observed significant improvements in cognitive performance for individuals exposed to nature. Urban soundscapes did not systematically affect performance either adversely or beneficially. Natural sounds did not differentially change positive or negative affect, despite these sounds being aesthetically preferred to urban sounds. These results provide initial evidence that brief experiences with natural sounds can improve directed attention functioning in a single experimental session.
Beyond ART, two broad research findings support potential cognitive benefits from experiencing nature sounds. First, prior studies have demonstrated widespread associations between noise levels and health. Noise pollution (e.g., urban environmental noises with sustained, high-amplitudes) has been associated with greater amounts of reported stress and distraction (e.g., de Paiva Vianna, Cardoso, & Rodrigues, 2015), which can lead to chronic learning and attention problems (see Hammer, Swinburn, & Neitzel, 2014). Thus, natural sounds may improve aspects of cognition relative to urban sounds because these two classes of sounds generally differ with respect to their amplitude in the real world (see McDonald et al., 1995), with nature sounds being thought to provide a quiet respite from urban environments (Mace, Bell, & Loomis, 2004). In this kind of framework, however, nature sounds may not confer any cognitive benefits relative to urban sounds when presented at the same amplitude.
A second reason why natural sounds may improve cognitive functioning is captured by stress reduction theory (SRT; Ulrich, 1983). SRT asserts that the aesthetic and affective value of experiences with nature can lower stress levels, which may in turn benefit cognitive performance. In support of SRT, natural sounds have been shown to reduce physiological symptoms of stress and improve affect (e.g., Alvarsson, Wiens, & Nilsson, 2010; Benfield, Taff, Newman, & Smyth, 2014; Ulrich et al., 1991), and, moreover, certain classes of natural sounds (birdsong) are perceived to both lower stress and restore attention (e.g., Ratcliffe, Gatersleben, & Sowden, 2013). Thus, nature-related benefits to cognitive functioning are compatible with both ART and SRT, though under SRT one would expect cognitive benefits to be a consequence of affective changes.
The present experiment provides a more direct test of whether randomly assigning participants to hear nature versus urban soundscapes improves the functioning of directed attention. In line with previous work from the visual domain (e.g., Berman et al., 2008; Berto, 2005; Bourrier, Berman, & Enns, 2018), the primary hypothesis was that brief experiences with nature sounds, relative to urban sounds, will result in performance improvements on cognitive tasks requiring directed attention.
To address whether any nature-related cognitive improvements could be explained by affective changes, which would be predicted under SRT, participants provided aesthetic ratings of the sounds they heard as well as rated their positive and negative affect before and after the sound intervention. Aesthetic judgments have been interpreted as an affective response in the context of SRT (Ulrich, 1983), and previous investigations of nature-related cognitive benefits in vision have examined how aesthetic ratings of experienced nature relate to cognitive improvements (Berman et al., 2008).
Given that prior research has established that nature stimuli are aesthetically preferred to urban stimuli (e.g., Kaplan, Kaplan, & Wendt, 1972; Kardan et al., 2015) and that experiences with nature can improve positive affect and reduce negative affect (e.g., Benfield et al., 2014; Bratman, Daily, Levy, & Gross, 2015), we hypothesized that, relative to urban sounds, nature sounds will: (1) be aesthetically preferred, (2) increase positive affect, and (3) decrease negative affect. Importantly, however, under SRT these aesthetic and affective changes should significantly relate to any observed cognitive improvements. Thus, there are two overarching aims of this work. The first aim is to assess whether nature sounds can improve aspects of cognitive performance. The second aim is to ground any observed nature-related cognitive benefits in the context of either ART or SRT.
The experiment adopted a 2 (time: pre-intervention, post-intervention) x 2 (soundscape: natural, urban) mixed factorial design, with time as the within-participant factor and soundscape as the randomly-assigned, between-participant factor.
After providing written consent, participants completed the PANAS, BDS, and DNB in this order. These pre-intervention assessments took approximately 20 minutes to complete. Participants then heard 40 natural or urban soundscapes, depending on the condition to which they were randomly assigned. This portion of the experiment took approximately 15 min to complete. Following the natural or urban sound exposure, participant retook the PANAS, BDS, and DNB in this order. Finally, participants filled out a brief questionnaire, which collected basic demographic information as well as required participants to write down their thoughts as to the purpose of the study, as well as whether they had participated in any similar study.
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