\u3cem\u3eGRASP News\u3c/em\u3e, Volume 8, Number 1

A report of the General Robotics and Active Sensory Perception (GRASP) Laboratory. Edited by Thomas Lindsay

Change blindness: eradication of gestalt strategies

Arrays of eight, texture-defined rectangles were used as stimuli in a one-shot change blindness (CB) task where there was a 50% chance that one rectangle would change orientation between two successive presentations separated by an interval. CB was eliminated by cueing the target rectangle in the first stimulus, reduced by cueing in the interval and unaffected by cueing in the second presentation. This supports the idea that a representation was formed that persisted through the interval before being 'overwritten' by the second presentation (Landman et al, 2003 Vision Research 43149–164]. Another possibility is that participants used some kind of grouping or Gestalt strategy. To test this we changed the spatial position of the rectangles in the second presentation by shifting them along imaginary spokes (by ±1 degree) emanating from the central fixation point. There was no significant difference seen in performance between this and the standard task [F(1,4)=2.565, p=0.185]. This may suggest two things: (i) Gestalt grouping is not used as a strategy in these tasks, and (ii) it gives further weight to the argument that objects may be stored and retrieved from a pre-attentional store during this task

Activity profiling for minimally invasive surgery

Imperial Users onl

Spatial and human factors affecting image quality and viewer experience of stereoscopic 3D in television and cinema

PhD ThesisThe horizontal offset in the two eyes’ locations in the skull means that they receive slightly different images of the world. The visual cortex uses these disparities to calculate where in depth different objects are, absolutely (physical distance from the viewer, perceived very imprecisely) and relatively (whether one object is in front of another, perceived with great precision). For well over a century, stereoscopic 3D (S3D) technology has existed which can generate an artificial sense of depth by displaying images with slight disparities to the different retinas. S3D technology is now considerably cheaper to access in the home, but remains a niche market, partly reflecting problems with viewer experience and enjoyment of S3D. This thesis considers some of the factors that could affect viewer experience of S3D content. While S3D technology can give a vivid depth percept, it can also lead to distortions in perceived size and shape, particularly if content is viewed at the wrong distance or angle. Almost all S3D content is designed for a viewing angle perpendicular to the screen, and with a recommended viewing distance, but little is known about the viewing distance typically used for S3D, or the effect of viewing angle. Accordingly, Chapter 2 of this thesis reports a survey of members of the British public. Chapters 3 and 4 report two experiments, one designed to assess the effect of oblique viewing, and another to consider the interaction between S3D and perceived size. S3D content is expensive to generate, hence producers sometimes “fake” 3D by shifting 2D content behind the screen plane. Chapter 5 investigates viewer experience with this fake 3D, and finds it is not a viable substitute for genuine S3D while also examining whether viewers fixate on different image features when video content is viewed in S3D, as compared to 2D.part-funded by BSkyB and EPSRC as a CASE PhD studentship supporting PH