PubMed · 11184235
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S A Spence. 2000. Between will and action.. https://doi.org/10.1136/jnnp.69.5.702
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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. It has further been argued that eye-movement planning and attentional orienting share common neural mechanisms. Electrophysiological studies have shown that the superior colliculus receives no direct projections from short-wave-sensitive cones (S cones), 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. However, when involuntary orienting was tested in a Posner cueing task, 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.
The human cortical visual system is organized into major pathways: a dorsal stream projecting to the superior parietal lobe (SPL), considered to be critical for visuospatial perception or on-line control of visually guided movements, and a ventral stream leading to the inferotemporal cortex, mediating object perception. Between these structures lies a large region, consisting of the inferior parietal lobe (IPL) and superior temporal gyrus (STG), the function of which is controversial. Lesions here can lead to spatial neglect, a condition associated with abnormal visuospatial perception as well as impaired visually guided movements, suggesting that the IPL+STG may have largely a "dorsal" role. Here, we use a nonspatial task to examine the deployment of visuotemporal attention in focal lesion patients, with or without spatial neglect. We show that, regardless of the presence of neglect, damage to the IPL+STG leads to a more prolonged deployment of visuotemporal attention compared to lesions of the SPL. Our findings suggest that the human IPL+STG makes an important contribution to nonspatial perception, and this is consistent with a role that is neither strictly "dorsal" nor "ventral". We propose instead that the IPL+STG has a top-down control role, contributing to the functions of both dorsal and ventral visual systems.
Paying attention can improve vision in many ways, including some very basic functions such as contrast discrimination, a task that probably reflects very early levels of visual processing. Electrophysiological, psychophysical, and imaging studies on humans as well as single recordings in monkey show that attention can modulate the neuronal response at an early stage of visual processing, probably by acting on the response gain. Here, we measure incremental contrast thresholds for luminance and color stimuli to derive the contrast response of early neural mechanisms and their modulation by attention. We show that, for both cases, attention improves contrast discrimination, probably by multiplicatively increasing the gain of the neuronal response to contrast. However, the effects of attention are highly specific to the visual modality: concurrent attention to a competing luminance, but not chromatic pattern, greatly impedes luminance contrast discrimination; and attending to a competing chromatic, but not luminance, task impedes color contrast discrimination. Thus, the effects of attention are highly modality specific, implying separate attentional resources for different fundamental visual attributes at early stages of visual processing.