Performance analysis of a compact auto-phoropter for accessible refractive assessment of the human eye.

We present the performance analysis and specifications of a portable auto-phoropter system that can be employed for fast refractive assessment of a large population. A customized Shack-Hartmann wavefront sensor is developed to accurately measure the defocus and astigmatism of the eye within ±10D and ±6D, respectively. Three fluidic lenses are designed to correct the vision in real time. A digital Snellen chart is integrated into the system to validate the accuracy of the measurement and the correction by means of achieving 20/20 vision. The refractive error of eight subjects (16 eyes) has been measured objectively (without patient's feedback) using the proposed system and the results are compared with their clinical prescription through the Bland-Altman method. It is shown that the auto-phoropter takes less than 8 s to measure and correct the eye refractive error with an accuracy of ±0.25D.

Parametric dog-bone-shaped tunable cylindrical fluidic lens.

Tunable spherical fluidic lenses are among the most essential components in adaptive optics. However, fabricating cylindrical tunable lenses has proven more challenging, mainly due to the difficulty in eliminating the defocus component. We demonstrate a parametric approach to minimize the defocus in cylindrical tunable fluidic lenses. We theoretically model and experimentally verify that a dog-bone-shaped tunable cylindrical fluidic lens exhibits almost pure cylindrical performance within the range of ${\pm{\rm 5D}}$ of astigmatism. We anticipate these results will facilitate the use of tunable cylindrical fluidic lenses in adaptive optics applications and particularly ophthalmic devices, where rapid and reliable wavefront correction is required.

"Touched" by light: event-related potentials (ERPs) to visuo-haptic stimuli in peri-personal space.

Parietal neuronal populations have been found which respond bimodally to visual and somatosensory input regarding one's own limbs or even perceived haptic input of a false limb (Graziano et al., Science 290:1782-1785, 2000). Further, neuronal populations have been observed which respond preferentially to visual stimuli presented in spatial congruence with our hands (Graziano, Proc Natl Acad Sci USA 96:10418-10421, 1999). In this study, we examined event-related potentials (ERPs) elicited by laser dots projected onto or above participants' index and middle fingers during a sustained-attention task. We hypothesized that visual stimuli projected onto the hand would elicit differences in ERP deflections related to sensory gating and categorization in comparison to when projected close to the hand. Participants responded via a footswitch to rare target flashes of light occurring on or directly above the middle finger of the attended hand. We found enhanced amplitudes of the N1 and P3 deflections when the stimuli fell onto the finger tips as opposed to above them. Furthermore, the N1 for unattended stimuli was less suppressed when the lasers were projected onto the fingers. Behaviorally, participants were less accurate to targets when the lasers fell onto the fingers. We conclude that when the lasers appear to "touch" the participants, they act to automatically draw participants' attention. Thus visual stimuli projected onto the fingers of the 'unattended' hand are harder to filter out, leading to decreases in accuracy during task performance.

Spatial filtering versus anchoring accounts of brightness/lightness perception in staircase and simultaneous brightness/lightness contrast stimuli.

J. Cataliotti and A. Gilchrist (1995) reported that, consistent with anchoring theory, the lightness of a black step in a reflectance staircase was not altered by moving a white step from a remote to an adjacent location. Recently, E. Economou, S. Zdravkovic, and A. Gilchrist (2007) reported data supporting three additional predictions of the anchoring model (A. Gilchrist et al., 1999): 1) equiluminant incremental targets in staircase simultaneous lightness contrast stimuli appeared equally light; 2) the simultaneous lightness contrast effect was due mainly to the lightening of the target on the black surround; and 3) the strength of lightness induction was greatest for darker targets. We investigated similar stimuli using brightness/lightness matching and found, contrary to these reports, that: 1) the relative position of the steps in a luminance staircase significantly influenced their brightness/lightness; 2) equiluminant incremental targets in staircase simultaneous brightness/lightness contrast stimuli did not all appear equally bright/light; 3) an asymmetry due to a greater brightening/lightening of the target on the black surround was not general; and 4) darker targets produced larger effects only when plotted on a log scale. In addition, the ODOG model (B. Blakeslee & M. E. McCourt, 1999) did an excellent job of accounting for brightness/lightness matching in these stimuli.

Coming to terms with lightness and brightness: effects of stimulus configuration and instructions on brightness and lightness judgments.

To recover surface reflectance and illuminance from the raw luminance signal, the visual system must use prior assumptions and strategies that make use of additional sources of information. Indeed, it has been found that depending on experimental conditions, lightness (apparent reflectance) may refer to judgments that are similar to brightness judgments (apparent luminance), that are similar to local brightness-contrast judgments, or that represent an independent third dimension of achromatic experience which exists only when the illumination across regions of the display is visibly non-uniform (L. E. Arend & B. Spehar, 1993a, 1993b). This means that lightness data generated in one experimental condition may not be comparable to lightness data measured in other conditions. We investigate this problem with regard to a history of data on simultaneous brightness-contrast by measuring brightness, brightness-contrast, and lightness in stimuli similar to those used in Gilchrist's edge-substitution studies (A. Gilchrist, S. Delman, & A. Jacobsen, 1983) and in stimuli similar to those used to test Gilchrist's intrinsic-image model against his newer anchoring model (A. Gilchrist, 2006). Our results clarify confusions that appear to stem from comparing different types of lightness judgments and from inadvertently using brightness as an index of lightness under conditions where independent lightness judgments are possible.