Hearing Silent Shapes: Identifying the Shape of a Sound-Obstructing Surface

Two experiments test whether the shape of objects that obstruct sound can be perceived by human listeners. Three foam-core shapes of equal area—disk, square, and triangle—were positioned in front a set of loudspeakers, which emanated broadband noise. On each trial, blindfolded listeners were asked to identify which shape obstructed the noise. Both experiments revealed that under most conditions, listeners could identify the shapes at better-than-chance levels. Experiment 2 also showed that the addition of a second intensity level of broadband noise randomized across trials actually improved performance. This finding suggests that listeners were likely basing their judgments on an acoustic dimension that was invariant—and was perhaps made more salient—over multiple intensities. These results add to the growing literature showing that human listeners are sensitive to sound-structuring surfaces that themselves do not produce sound.