Eye movements present the visual system with the challenge of providing the experience of a stable world. This appears to require the location of objects to be mapped from retinal to head and body referenced coordinates. Following D. Burr, A. Tozzi, and M. C. Morrone (2007), here we address the issue of whether adaptation-based duration compression (A. Johnston, D. H. Arnold, & S. Nishida, 2006) takes place in a retinocentric or head-centric frame of reference. Duration compression may be associated with shifts in apparent temporal frequency. However, using an adaptation schedule that minimizes any effect of adaptation on apparent temporal frequency, we still find substantial apparent duration compression. Duration compression remains when the adaptor continuously translates in head-centered coordinates but is fixed on the retina, isolating retinal adaptation. Apparent duration was also measured after a change in gaze direction-a strategy which allows eye-centered and head-centered components of adaptation-induced duration compression to be distinguished. In two different paradigms, we found significant compression was elicited by retinotopic adaptation, with no significant change in apparent duration following spatiotopic adaptation. We also observed no interocular transfer of adaptation. These findings point to an early locus for the adaptation-based duration compression effect.

Temporal processing is traditionally dissociated from spatial vision. Recent evidence, however, has shown that adaptation to high temporal frequency (D. Burr, A.Tozzi, & M. C. Morrone, 2007; A. Johnston, D. H. Arnold, & S. Nishida, 2006; A. Johnston et al., 2008) induces spatially specific reductions in the apparent duration of subsecond intervals containing medium frequency drift or flicker. Here we examine the spatial tuning of these temporal adaptation effects. Our results show that duration compression is tightly tuned to the spatial location of the adaptor and can be induced by very narrow adaptors. We also demonstrate that the effects of adaptation on perceived duration are dissociable from those on apparent temporal frequency, which suggests early but separate influences of temporal frequency adaptation on time and speed perception.

In this study, we show that invisible flicker adaptation reduces the perceived duration of a subsequently viewed stimulus in control subjects, but not in dyslexics. Dyslexics, like controls, show apparent duration compression after 20Hz flicker and show normal shifts in apparent temporal frequency after adaptation. However a subgroup of the test group, scoring low on both a test of phonological skill (spoonerisms) and a test of literacy (NART), show an apparent temporal expansion after 5Hz flicker adaptation, a finding not previously seen in controls. Recent studies have linked genes conferring susceptibility to a cluster of language and sensory deficits to anomalous neural migration, providing a tentative biological basis for dyslexia. However it has proved difficult to establish a clear link between sensory deficits and impaired reading. The results presented here point to an abnormal adaptation response within the early precortical stages of the magnocellular pathway, occurring in tandem with a deficit in word-level cognitive processing, providing psychophysical evidence for anomalous cortico-thalamic circuits in dyslexia.

Brief stimuli presented near the onset of saccades are grossly mislocalized in space. In this study, we investigated whether the Bayesian hypothesis of optimal sensory fusion could account for the mislocalization. We required subjects to localize visual, auditory, and audiovisual stimuli at the time of saccades (compared with an earlier presented target). During fixation, vision dominates and spatially "captures" the auditory stimulus (the ventriloquist effect). But for perisaccadic presentations, auditory localization becomes more important, so the mislocalized visual stimulus is seen closer to its veridical position. The precision of the bimodal localization (as measured by localization thresholds or just-noticeable difference) was better than either the visual or acoustic stimulus presented in isolation. Both the perceived position of the bimodal stimuli and the improved precision were well predicted by assuming statistically optimal Bayesian-like combination of visual and auditory signals. Furthermore, the time course of localization was well predicted by the Bayesian approach. We present a detailed model that simulates the time-course data, assuming that perceived position is given by the sum of retinal position and a sluggish noisy eye-position signal, obtained by integrating optimally the output of two populations of neural activity: one centered at the current point of gaze, the other centered at the future point of gaze.

Under conditions of short-term saccadic adaptation, stimuli presented long before saccadic onset are perceptually mislocalized in space. Here we study whether saccadic adaptation can also affect localization of objects by pointing. We measured localization performance during fixation and after normal saccades and adapted saccades, for a bar presented well before a saccadic eye movement, for both pointing and verbal localization, under open-loop conditions generated by a transient dark period about 300 ms after the presentation of the bar. During fixation and normal saccade, localization performance for verbal report was veridical, while for pointing there was an overestimation of the target eccentricity respect to gaze, in agreement with the idea of separate representations of space for action and perception. During saccadic adaptation, there was a significant shift of both pointing and verbal report localization in the direction of adaptation with similar spatial selectivity for both tasks. These results indicate that saccadic adaptation induces a similar re-calibration of the action map as well as of the perceptual map, suggesting a common site of operation in the transformation from eye-centered to gaze-centered coordinates.