EFFECTS OF A STATIC TEXTURED BACKGROUND ON MOTION INTEGRATION

We studied how the visual system integrates locally ambiguous velociti es into global unambiguous coherent motion in the presence or absence of a textured background, Line drawings of complex figures were presen ted through invisible (i.e. same luminance and hue as the background) circular apertures such that only straight line segments were visible, These figures were either presented against a uniform background or e mbedded in static textures made of similar line segments in such a way that figures cannot be detected if they remain static, Under our expe rimental conditions, the figures translated clockwise or counterclockw ise along a circular path and observers were required to discriminate the global direction of motion, Because of the aperture problem, a sin gle moving segment cannot disambiguate the global direction of the fig ures and integration across multiple line segments is therefore necess ary to perform the task, We found that with figures at high contrast, the presence of a texture enhanced direction discrimination, while dir ection discrimination of figures at low contrast was impaired by the p resence of the texture, These paradoxical effects of a static texture were further tested by manipulating the relative contrast between figu res and texture, the motion onset asynchrony (the delay between stimul us onset and motion onset or MOA), the density, the orientation and th e distribution of texture elements, The effects of the texture, either facilitation or suppression, increase with texture contrast, Accuracy improves with MOA and decreases with texture density, In general, at high figure contrast, accuracy is better whenever referents are presen t in the image, We suggest that facilitation by the texture at high fi gure contrast is accounted for by reduced salience of segmentation cue s such as line terminators and increased accuracy of local velocity me asurements, On the other hand, decreased performance at low figure con trast may reflect lateral suppression of the responses to motion signa ls by the texture