Feature selectivity of visual cortical responses measured during passive fixation provides only a partial view of selectivity because it does not account for the influence of cognitive factors. Here we focus on primate area V4 and ask how neuronal tuning is modulated by task engagement. We investigated whether responses to colored shapes during active shape discrimination are simple, stimulus-agnostic, scaled versions of responses during passive fixation, akin to results from attentional studies. Alternatively, responses could be subject to stimulus-specific scaling, that is, responses to different stimuli are modulated differently, resulting in changes in underlying shape/color selectivity. Among 83 well-isolated V4 neurons in two male macaques, only a minority (16 of 83), which were weakly tuned to both shape and color, displayed responses during fixation and discrimination tasks that could be related by stimulus-agnostic scaling. The majority (67 of 83), which were strongly tuned to shape, color, or both, displayed stimulus-dependent response changes during discrimination. For some of these neurons (39 of 83), the shape or color of the stimulus dictated the magnitude of the change, and for others (28 of 83) it was the combination of stimulus shape and color. Importantly, for neurons with one strong and one weak tuning dimension, stimulus-dependent response changes during discrimination were associated with a relative increase in selectivity along the stronger tuning dimension, without changes in tuning peak. These results reveal that more strongly tuned V4 neurons may also be more flexible in their selectivity, and imbalances in selectivity are amplified during active task contexts.

SIGNIFICANCE STATEMENT Tuning for stimulus features is typically characterized by recording responses during passive fixation, but cognitive factors, including attention, influence responses in visual cortex. To determine how behavioral engagement influences neuronal responses in area V4, we compared responses to colored shapes during passive fixation and active behavior. For a large fraction of neurons, differences in responses between passive fixation and active behavior depended on the identity of the visual stimulus. For a subgroup of strongly feature-selective neurons, this response modulation was associated with enhanced selectivity for one feature at the expense of selectivity for the other. Such flexibility in tuning strength could improve performance in tasks requiring active judgment of stimuli.

被动注视过程中测量的视觉皮层反应的特征选择性仅提供选择性的部分视图，因为它没有考虑认知因素的影响。在这里，我们重点关注灵长类动物 V4 区域，并探讨任务参与如何调节神经元调节。我们研究了主动形状辨别过程中对彩色形状的反应是否是简单的、与刺激无关的、被动固定过程中反应的缩放版本，类似于注意力研究的结果。或者，响应可能会受到特定于刺激的缩放的影响，即对不同刺激的响应进行不同的调节，从而导致潜在的形状/颜色选择性的变化。在两只雄性猕猴的 83 个隔离良好的 V4 神经元中，只有少数（83 个中的 16 个）对形状和颜色的调节较弱，在注视和辨别任务中表现出反应，这些反应可能与刺激不可知的尺度有关。大多数（83 人中的 67 人）对形状、颜色或两者都有强烈的调节，在辨别过程中表现出依赖于刺激的反应变化。对于其中一些神经元（83 个中的 39 个）来说，刺激的形状或颜色决定了变化的幅度，而对于其他神经元（83 个中的 28 个）来说，刺激的形状或颜色决定了刺激形状和颜色的组合。重要的是，对于具有一个强调节维度和一个弱调节维度的神经元，辨别过程中刺激依赖性反应的变化与沿较强调节维度选择性的相对增加相关，而调节峰值没有变化。这些结果表明，调节更强烈的 V4 神经元的选择性也可能更灵活，并且选择性的不平衡在活动任务环境中会被放大。

意义声明对刺激特征的调节通常以记录被动注视期间的反应为特征，但包括注意力在内的认知因素会影响视觉皮层的反应。为了确定行为参与如何影响 V4 区的神经元反应，我们比较了被动固定和主动行为期间对彩色形状的反应。对于大部分神经元来说，被动注视和主动行为之间的反应差异取决于视觉刺激的身份。对于强特征选择性神经元的亚群来说，这种反应调节与对一个特征的选择性增强相关，但牺牲了对另一个特征的选择性。这种调整强度的灵活性可以提高需要主动判断刺激的任务的表现。