Differences between naïve and expert observers’ vergence and accommodative responses to a range of targets

Horwood,A, Riddell,P. Opth & Physiol.Optics 2010,30, 152-159

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People with a knowledge of the eye and visual experiments accommodate and converge better than naïve observers. “Experts” should not be used if typical responses are required as controls.


Vergence and accommodation studies often use adult participants with experience of vision science. Reports of infant and clinical responses are generally more variable and of lower gain, with the implication that differences lie in immaturity or sub-optimal clinical characteristics but expert /naïve differences are rarely considered or quantified.


16 undergraduates, naïve to vision science were individually matched by age, visual acuity, refractive error, heterophoria, stereoacuity and near point of accommodation to 2nd & 3rd year orthoptics and optometry undergraduates (“experts”). Accommodation and vergence responses were assessed to targets moving between 33cm, 50 cm, 1m and 2m using a haploscopic device incorporating a PlusoptiX SO4 autorefractor. Disparity, blur and looming cues were separately available or minimised in all combinations. Instruction set was minimal.


In all cases, vergence and accommodation response slopes (gain) were steeper and closer to 1.0 in the expert group (p=0.001), with less lag for near targets (p=0.012). For vergence, the differences between expert and naïve response slopes increased with increasingly open-loop targets (linear trend p=0.025). Although we predicted that proximal cues would drive additional response in the experts, the proximity-only cue was the only condition that showed no statistical effect of experience.


Expert observers provide more accurate responses to near target demand than matched naïve observers. We suggest that attention, practice, voluntary and proprioceptive effects may enhance responses in experienced participants when compared to a more typical general population. Differences between adult reports and the developmental and clinical literature may partially reflect expert / naïve effects, as well as developmental change. If developmental and clinical studies are to be compared to adult normative data, uninstructed naïve adult data should be used.