Tuesday, October 14, 2014

Sound-contingent visual motion aftereffect

Hidaka, S., Teramoto, W., Kobayashi, M., & Sugita, Y. (2011). Sound-contingent visual motion aftereffect. BMC Neuroscience,12, 44. doi:http://dx.doi.org/10.1186/1471-2202-12-44

The authors analyze the new neural connections that can be created after a brief (3 min) exposure to simultaneous motion signals and sound frequencies. The main purpose of the study is to prove that the brain, regardless of age, can create interconnections between sound and movement when exposed to certain stimulus. They also prove how these interconnections are still present after 2 days of being exposed. This principle is based in the fact that visual movements are usually accompanied by some sound in real life. They emphasize in the concept of “contingent motion aftereffect” referring as an effect that is still present after a previous stimulus. More specifically, the authors refer to how the brain can easily associate information from combined sensory inputs. In their experiment they test how the brain can associate a series of dots moving in certain directions (left and right) with two different sound frequencies (2 kHz and 500 Hz).
In the first stage of the experiment the participants had to look at an area containing several dots moving in different directions every 500ms. The dots' movement coherence was alternated: 0%, 3.75%, 7.5% 15% or 30% moving leftwards or rightwards, while the rest of the dots were moving in random directions. The participants had to determine in which direction the majority of the dots were moving (left or right). During this phase, participants had an auditory stimulus of 500ms duration alternating randomly from 2 kHz or 500 Hz unrelated to dot movement. The second phase of the experiment consisted in exposing the participants to a similar experiment but with a 100% movement coherence (all points move either to the right or to the left). In this phase, high frequency 2 kHz is synchronized with leftward movement while low frequency is synchronized with rightward dot movement. The participants were exposed to these audio visual stimuli during 3 minutes. In the third stage of the test, participants were exposed to the same test as in the beginning (random movement, and no relation between tones and movement direction).
In order to determine the effects to the exposure, researchers elaborated a series of statistical tests to determine the failure of participants to determine the real direction of movement before and after the 3 min exposure. In this analysis they also included the results obtained when participants had no auditory stimulus. Surprisingly, results showed that the participant’s visual motion perception was heavily affected after the second phase of the test when they were exposed to direct correlation between movement and tones, meaning that their ability to identify the direction of movement was diminished. When they were hearing the 2 kHz tone they perceived it as a right movement regardless of real direction and vice versa with the low 500 Hz frequency. More importantly, this effect remained present after two days when the participants were tested again.


One important thing to notice is the short length of exposure vs. the effect duration.  So, if this kind of effect can be achieved under this short exposure to repeated sounds and images I wonder what would be the effect on doing this repetitively, once per day for example. Moreover, it will be interesting to see how this concept can be used in learning techniques or to improve some particular skills. I also found quite interesting how the authors discuss the validity of the results by comparing them with other studies that might suggest that the responses might be biased when the visual input is not completely clear. They reject the possibility of having a “biased decision” because of the participant uncertainty by doing additional focused vision tests. Nevertheless this particular experiment is based in the fact that there are no other visible objects in the periphery which is far from reality. I believe this kind of studies that explore the ability of the brain to create new neural representations relating sound and movement could be potentially useful for improving certain skills considering all the audio/visual media we are exposed every day.

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