This disclosure provides systems, methods and apparatus, including computer programs encoded on computer storage media, for sensing touch and/or gestures in the near-field area overlying a light-guiding layer within a device or other optical sensing system. In one aspect, modulated infrared light is emitted into the overlying area, and the light reflected by objects within the overlying area is redirected through the light-guiding layer to infrared sensors. In one aspect, a masking structure can be located between the light-guiding layer and the infrared sensors. In some aspects, probability mapping or backtracing can be used to estimate the locations of objects within the overlying area.