Unilateral spatial neglect (USN) is the failure to report, respond, or orient to novel or meaningful stimuli presented on the side opposite a brain lesion. In our previous study, we reported that the ability of patients with USN to perform when the neck was fixed (called cognitive ability) was different from that when the neck was not fixed (called exploratory ability). However, the exploratory ability index has not been clarified, and cognitive and exploratory abilities have not been quantified. Thus, in this study, we identified neck movement as an exploratory ability index for patients with USN. Furthermore, we proposed equations to quantify cognitive and exploratory abilities and suggested that these equations can be used to understand patients' neglect symptoms in more detail. These findings revealed that the two evaluations of cognitive and exploratory abilities are crucial in USN evaluation and are key to individualizing intervention for each patient.