Visual Functions

Principle investigators: Stephanie Jainta, Edmund Wascher
Staff: n.a.
Funds: n.a.  
Cooperation/Partners: Simon P. Liversedge (University Southampton); Hazel. I. Blythe (University Southampton); Tara Alvarez (NJIT, USA)

Uptake and initial processing of visual information determine signal quality and, in consequence, the quality of the percept that is aware to the receiver. Any understanding of visual perception needs to acknowledge that only a very small part of the very rich, always present and surrounding visual information is actually used. This information is (mainly) found on the foveal part of the retina. Only less then a degree away from the centre of the fovea, the visual resolution declines rapidly (Howard, 2012, Leigh & Zee, 2006). Such decline necessitates eye movements that bring images onto the foveal part of the retina, before high quality visual information can be extracted and then channelled forward for efficient cognitive processing.

In this context, saccadic eye movements serve to redirect the visual axes to a new location; in parallel, vergence eye movements allow us to coherently merge the visual input received by each eye so that finally a single percept (including 3D depth perception) is achieved (Schor & Ciuffreda, 1983). All eye movements also always work in synchrony with early optic adjustments (accommodation, i.e. the focusing of the lens, for example) to maintain single and clear vision (Howard, 2012, Leigh & Zee, 2006). In natural viewing all these eye movements occur up to 4 times per second and are interspersed with brief periods of relative stillness of the eyes (fixations). These fixation phases are the critical periods of vision during which information is primarily encoded (Howard, 2012, Leigh & Zee, 2006, Liversedge & Findlay, 2000, Rayner, 1998). Thus, initial optic and oculomotor adjustments as well as early visual processing determine the overall signal quality and, finally, the percept that is aware to the receiver.

In the past, eye movement related aspects of visual perception and early neurophysiological processing has been addressed separately. But in natural viewing situations particular information is actively selected for foveation – based on its behavioral relevance (top-down factors) or images qualities, i.e. sensory cues (bottom-up factors).
Binocular advantages in reading. Reading itself is an essential skill for successful function in today’s society and, typically, humans make use of both of their eyes in reading. It has been shown that the timely delivery of high quality, binocular visual information is critical for effective reading (Jainta et al., 2014, Jainta & Jaschinski, 2012, Liversedge et al., 2006, Nuthmann & Kliegl, 2009), but, yet, no specific characteristic of the visual process has been framed as basis of such specific binocular benefits. We will investigate whether early summation effects (Blake et al.,1981) of primary visual features and derivates (Howard, 2012) are critical for binocular advantages in reading, thus reflecting very early benefits at this vision-cognition interface. This research will be partly realized in cooperation with Prof. S. Liversedge (University of Southampton/U.K.) while jointly supervising the PhD thesis of Ms. M. Nikolova (University of Southampton/U.K.). Furthermore, we will address the range of binocular benefits for readers with reduced or disabled binocular vision, that is before and after strabismus operations in a cooperation with Prof. Dr. M. Abegg (Insel-Spital Bern/Switzerland).

Binocular vision in the context of digital eye strain. Society is becoming more dependent on smaller hand-held electronic devices, which require sustained vision – but the human visual system is not ready to deal with such demanding situations on a regular basis: In 2014, popular media reported that 75 % of media users suffer from digital eye strain (asthenopia). Previous research showed that vergence eye movements relate to astenopia (Leigh & Zee, 2006), but, unfortunately, current vergence models (Maxwell et al., 2010, Semmlow & Hung, 1980) show critical limitations and many aspects are not yet fully understood. In cooperation with Prof. Dr. T. Alvarez (NJIT, Newark/USA) we will develop a more complete model of vergence eye movements by incorporating aspects of accommodation (focusing of the lense), age and ideas of the innveration of the two eyes (Hering versus Helmholtz; see Howard (2012) or King & Zhou (2000)) to better predict digital eye strain (joined proposal BMBF-NSF-call; review results are pending).

Is a binocular advantage a binocular advantage or a monocular disadvantage? Binocular vision leads to direct binocular advantages when compared to monocular vision (Jainta et al., 2014, Schor & Ciuffreda, 1983, Sheedy et al., 1986; Steinman et al., 2000). Monocular vision is a special viewing condition since it does involve both cortical hemispheres (due to the optic chiasm) and also some potential rivalry regarding the input from the other eye (being a blank black or white screen or frame). Based on previous reports (see, for example, Roeber & Schröger, 2014 or Mohr et al., 2007), binocular rivalry is latest resolved in extrastriate visual areas and furthermore, bilateral redundancy gains (i.e. better performances in bilateral stimulus presentations) occur at latencies around 200 ms. Still, one question remains: how does the brain join its forces across both hemispheres in normal function and when do binocular advantages kick in? We will address this question in studies combining EEG-methods with haploscopic presentations and, finally, eye tracking setups to pin down the time course of binocular advantages.

Publications:

Jainta S, Blythe HI, Liversedge SP: Binocular advantages in reading. Curr Biol 24: 526-530 (2014)
http://dx.doi.org/10.1016/j.cub.2014.01.014

Jainta S, Jaschinski W: Individual differences in binocular coordination are uncovered by directly comparing monocular and binocular reading conditions. Invest Ophthalmol Vis Sci 53: 5762-5769 (2012)
http://dx.doi.org/10.1167/iovs.12-9707

Jainta S, Dehnert A, Heinrich SP, Jaschinski W: Binocular coordination during reading of blurred and nonblurred text. Invest Ophthalmol Vis Sci 52: 9416-9424 (2011)
http://dx.doi.org/10.1167/iovs.11-8237

Jainta S, Jaschinski W, Wilkins AJ: Periodic letter strokes within a word affect fixation disparity during reading. J Vision 10(13):2, 1-11 (2010)
http://www.journalofvision.org/content/10/13/2