In other words, the saccade target seems to attract the flashed probe, a phenomenon known as saccadic compression of space. Indeed, dramatic position errors are reported for a probe stimulus that is briefly flashed around the time of a saccade: the probe is perceived closer to the target of the imminent eye movement than it actually is (e.g., Honda, 1993, 1999 Morrone et al., 1997 Ross et al., 1997 Lappe et al., 2000). The perceived locations of probes around the time of saccadic eye movements have long been studied for the insight they give us about how spatial coordinates are updated when the retinal image shifts. ![]() After all, even stimuli that we scarcely see are seen at particular locations-they do not float in our visual experience as ungrounded percepts. These errors may reveal the mechanisms that the visual system uses to localize objects that have poor position or rapidly changing information. Despite the explicit location information provided by these spatial maps, objects are sometimes seen at positions other than their true locations. The visual system has many retinotopically organized representations of the visual field that could encode object locations ( Wandell et al., 2007). Understanding how we perceive and construct the visual space around us is a fundamental task in vision science with a long tradition in philosophy, psychology, neuroscience and other disciplines (see Khurana and Nijhawan, 2010 Melcher, 2011). Our experiments suggest that compression reflects how the visual system localizes weak targets in the context of highly visible stimuli. Finally, in Experiment 3, we found that compression decreased as probe duration increased both for masks and saccades although here we did find some evidence that factors other than simply visibility as we measured it contribute to compression. Comparing mislocalizations at different probe detection rates across masking, saccades and low contrast conditions without mask or saccade, Experiment 2 confirmed this observation and showed a strong influence of probe contrast on compression. To obtain compression without a mask, the probe had to be presented at much lower contrasts than with masking. Compression effects were found in all conditions. In all conditions, we adjusted probe contrast to make the probe equally hard to detect. In a first experiment, we varied the regions of the screen covered by a transient mask, including areas where no stimulus was presented and a condition without masking. Both of these degrade the probe visibility but we show that low probe visibility alone causes compression in the absence of any disruption. Here, we ask whether spatial compression depends on the transient disruptions of the visual input stream caused by either a mask or a saccade. More recently, we have demonstrated that brief probes are attracted towards a visual reference when followed by a mask, even in the absence of saccades ( Zimmermann et al., 2014a). Stimuli briefly flashed just before a saccade are perceived closer to the saccade target, a phenomenon known as perisaccadic compression of space ( Ross et al., 1997).
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