Signals invisible to the collicular and magnocellular pathways can capture visual attention

The retinal projection to the superior colliculus is thought to be important both for stimulus-driven eye movements and for the involuntary capture of attention [1-5]. It has further been argued that eye-movement planning and attentional orienting share common neural mechanisms [6-12]. Electrophysiological studies have shown that the superior colliculus receives no direct projections from short-wave-sensitive cones (S cones) [13-15], and, consistent with this, we found that irrelevant peripheral stimuli visible only to S cones did not produce the saccadic distractor effect produced by luminance stimuli [16, 17]. However, when involuntary orienting was tested in a Posner cueing task [18, 19], the same S-cone stimuli had normal attentional effects, in that they accelerated or delayed responses to subsequent targets. We conclude that involuntary attentional shifts do not require signals in the direct collicular pathway, or indeed the magnocellular pathway, as our S-cone stimuli were invisible to this channel also.