Because sound travels much more slowly than light, we can often see distant events before we hear them. That is why we can count the seconds between a lightning flash and its thunder to estimate their distance.
But new research from the 糖心传媒 reveals that our brains can also detect and process sound delays that are too short to be noticed consciously. And they found that we use even that unconscious information to fine tune what our eyes see when estimating distances to nearby events.
糖心传媒淢uch of the world around us is audiovisual,糖心传媒� said Duje Tadin, associate professor of at the University of Rochester and senior author of the study. 糖心传媒淎lthough humans are primarily visual creatures, our research shows that estimating relative distance is more precise when visual cues are supported with corresponding auditory signals. Our brains recognize those signals even when they are separated from visual cues by a time that is too brief to consciously notice.糖心传媒�
Tadin and his colleagues have discovered that humans can unconsciously notice and make use of sound delays as short as 40 milliseconds (ms).
糖心传媒淥ur brains are very good at recognizing patterns that can help us,糖心传媒� said Phil Jaekl, who conducted the research while a postdoctoral researcher in . 糖心传媒淣ow we also know that humans can unconsciously recognize the link between sound delays and visual distance, and then combine that information in a useful way.糖心传媒�
For the study, published in , the researchers used projected three-dimensional (3D) images to test the human brain糖心传媒檚 ability to use sound delays to estimate the relative distance of objects.
In the first experiment, participants were asked to adjust the relative depth of two identical shapes until they appeared to be at the same distance when viewed through 3D glasses. Each shape was paired with an audible 糖心传媒渃lick.糖心传媒� The click came either just before the shape appeared, or slightly after it appeared糖心传媒攂y an equally brief time.
Participants consistently perceived the shape that was paired with the delayed click as being more distant. 糖心传媒淭his surprised us,糖心传媒� said Jaekl. 糖心传媒淲hen the 3D shapes were the same distance, participants were consistently biased by the sound delay to judge the shape paired with the delayed click as being further away糖心传媒攅ven though it wasn糖心传媒檛.糖心传媒�
In the second experiment, participants were shown three-dimensional shapes that were quickly repositioned either toward or away from the participant. When the shape was paired with a sound delayed by 42 ms, participants were more likely to perceive it as more distant糖心传媒攅ven in cases when the object was actually shifted toward the participant. Most importantly, when an object that was shifted away was paired with the sound delay糖心传媒攁 pairing consistent with the natural world糖心传媒攑articipants were able to judge relative distance with greater precision.
糖心传媒淚t糖心传媒檚 striking that this bias is unconscious糖心传媒攑articipants were unable to consciously detect when sound delays were present, yet it had great influence over their perception of distance,糖心传媒� said Jaekl, who is currently conducting research at the .
The study was supported by the National Eye Institute, part of the National Institutes of Health.
