Geeraerts Sarah, Michiels Karla, Lafosse Christophe, Vandenbussche Erik, Verfaillie Karl
Laboratory of Neuropsychology, University of Leuven, Belgium.
Neuropsychologia. 2005;43(4):542-53. doi: 10.1016/j.neuropsychologia.2004.07.011.
Visual extinction was investigated in six right brain-damaged patients with left visual neglect, using a psychophysical paradigm. Orientation discrimination thresholds were determined for both left and right hemifield gratings presented either in isolation or simultaneously with a contralateral distractor grating. To minimize the influence of possible sensory-perceptual deficits, the luminances of both target and distractor gratings were chosen to be 20 times the luminances necessary to discriminate between horizontal and vertical grating orientations. When the visibility of target and distractor gratings was subjectively equalized in this way, neglect patients still showed a significant extinction effect, i.e. a significant interference of the right hemifield distractor with left hemifield orientation sensitivity. By manipulating the luminances of left and right hemifield gratings during bilateral simultaneous stimulus presentation, we demonstrated the role of luminance-contrast imbalances in eliciting visual extinction. Both decreasing the right distractor luminance and increasing the left target stimulus luminance resulted in an elimination of the observed extinction effects. These results show that not the absolute salience of one of two simultaneously presented stimuli, but the relative salience of both stimuli, is the crucial factor for inducing extinction.
采用心理物理学范式，对6例患有左侧视觉忽视的右脑损伤患者的视觉消弱现象进行了研究。分别测定了单独呈现以及与对侧干扰光栅同时呈现时左、右半视野光栅的方向辨别阈值。为了尽量减少可能的感觉-知觉缺陷的影响，将目标光栅和干扰光栅的亮度都设置为区分水平和垂直光栅方向所需亮度的20倍。当以这种方式使目标光栅和干扰光栅的可见度在主观上达到平衡时，忽视患者仍表现出显著的消弱效应，即右半视野干扰物对左半视野方向敏感性存在显著干扰。通过在双侧同时呈现刺激时操纵左、右半视野光栅的亮度，我们证明了亮度对比失衡在引发视觉消弱中的作用。降低右侧干扰物亮度和增加左侧目标刺激亮度均导致观察到的消弱效应消失。这些结果表明，诱发消弱的关键因素不是两个同时呈现的刺激之一的绝对显著性，而是两个刺激的相对显著性。
