The orientation discrimination deficit in strabismic amblyopia depends upon stimulus bandwidth

We show that the previously reported orientation deficit in amblyopia (Skot tun, B. C., Bradley, A., & Freeman, R. D. (1986). Orientation discriminatio n in amblyopia. Investigative Ophthalmology and Visual Science, 30, 532-537 ) also occurs for arrays of randomly positioned Gabor micropatterns for whi ch explanations based on either neural disarray or local neural interaction s would not hold. Furthermore, when using Gabors, we show that the deficit varies with the spatial frequency and orientational bandwidth of the stimul i used to measure it. We discuss two competing explanations for this, one b ased on a broader underlying detector bandwidth in amblyopia (both orientat ion and spatial frequency) and the other based on a selective deficit of fi rst-order, as opposed to second-order orientation processing in strabismic amblyopia. Our results favour the latter interpretation. (C) 1999 Elsevier Science Ltd. All rights reserved.