Sensitivity to biological motion drops by ∼1/2 log-unit with inversion, and is unaffected by amblyopia

Abstract

The low-level deficits associated with amblyopia have been studied extensively, but very little is known about potential impairments to higher-level visual processing such as object recognition or structure-from-motion. Studies on biological motion, a complex form of structure-from-motion depicting human actions, have demonstrated that normal observers can analyze these patterns more effectively when they are shown in their original upright configuration as opposed to inverted upside-down (feet-up head-down). We measured this inversion effect quantitatively for both the dominant and amblyopic eyes of amblyopic observers. We found a modest ( approximately 30%) loss in sensitivity in the amblyopic eye for both upright and inverted actors, which we attribute to low-level deficits. However, we found no difference in the inversion effect between the two eyes, both showing an average 1/2 log-unit drop in sensitivity between upright and inverted displays. Our data provide a quantitative estimate of the inversion effect for biological motion, and demonstrate that higher-level processing in the motion hierarchy is not affected by amblyopia.

Sensitivity to synchronicity of biological motion in normal and amblyopic vision

“…4B) eyes. Our findings reveal that like normal observers, amblyopes are more sensitive to synchronized versus desynchronized interactions, indicating that the higher-level processing of biological motion remains intact, as previously reported (Neri, Luu, & Levi, 2007; Thompson et al, 2008). …”

“…The increased sample threshold is not the result of low-level losses (dot trajectories were highly visible) but may reflect losses in feature integration due to undersampling in the amblyopic visual system (Levi & Klein, 1986; Levi, Klein, & Sharma, 1999; Levi, Klein, & Yap, 1987). However, like normal observers, amblyopes are more sensitive to synchronized versus desynchronized interactions, indicating that higher-level processing of biological motion remains intact, as previously reported (Neri, Luu, & Levi, 2007; Thompson et al, 2008). Similar to normal vision, in amblyopia the difference in biological motion perception between synchronized and desynchronized stimuli is due to the disruptive effect of desynchronization on the perception of biological motion.…”

“…Different performance metrics have been used to measure biological motion detection in amblyopic observers. Using fully sampled stimuli while varying the amount of scrambling (Thompson et al, 2008) and measuring the inversion effect with the addition of masking noise dots (Neri, Luu, & Levi, 2007) have proven to be effective methods of measurement. This study extends upon these findings and establishes varying the number of displayed joints to determine the threshold number of dot trajectories as another performance metric that can be used in the quantitative analysis of biological motion detection in amblyopic observers.…”

“…However, it is unclear whether these extrastriate cortical regions serve to amplify the losses that occur in V1, or if the downstream losses are simply the reflection of the original losses in V1. Previous studies have demonstrated that higher-level visual processing such as for biological motion, a complex form of structure-from-motion representing humanactions, is unaffected by amblyopia (Neri, Luu, & Levi, 2007). …”

“…Previous studies investigating the effects of amblyopia on higher-level cognitive functions have found that biological motion detection as processed by global form from motion (Neri, Luu, & Levi, 2007) and local motion information (Thompson et al, 2008) is relatively unaffected. In human observers with normal vision, visual discrimination of a human agent is influenced by the presence of a second agent and by whether the two agents interact in a meaningful and synchronized way, such as during a dancing or fighting routine (Neri, Luu, & Levi, 2006).…”