A method for assessing the nervous system of a subject, the method comprising: presenting a sequence of selected individual stimuli from at least one stimulus ensemble to the nervous system of a subject at multiple locations adapted to evoke pupillary responses in at least one pupil of the subject, said stimulus ensemble comprising a plurality of individual stimuli, selected individual stimuli being concurrently presented in the sequence, the individual stimuli each being individually balanced such that the pupillary responses evoked by individual stimuli in the ensemble are balanced according to the strength of the neural responses evoked by the individual stimuli; detecting using a sensor (18, 19) responses of at least one pupil evoked by the stimuli; and relating the detected pupillary responses to the function of the subject's neural responses to at least two of the individual stimuli of the ensemble; wherein: (a) the stimuli are visual stimuli presented to a subject at multiple locations in the visual field of one or both of the subject's eyes, the resulting set of pupillary responses providing a map of visual function across the visual field of the one or both eyes; (b) the ensemble of visual stimuli is a multifocal stimuli ensemble, the appearance or non-appearance of individual stimuli in the ensemble or other modulations of the stimuli being controlled by statistically independent sequences; and (c) the individual stimuli are each individually balanced such that responses of the pupils to more effective stimuli in the ensemble are reduced to enable larger responses of the pupils to less effective stimuli. presenting a sequence of selected individual stimuli from at least one stimulus ensemble to the nervous system of a subject at multiple locations adapted to evoke pupillary responses in at least one pupil of the subject, said stimulus ensemble comprising a plurality of individual stimuli, selected individual stimuli being concurrently presented in the sequence, the individual stimuli each being individually balanced such that the pupillary responses evoked by individual stimuli in the ensemble are balanced according to the strength of the neural responses evoked by the individual stimuli; detecting using a sensor (18, 19) responses of at least one pupil evoked by the stimuli; and relating the detected pupillary responses to the function of the subject's neural responses to at least two of the individual stimuli of the ensemble; wherein: (a) the stimuli are visual stimuli presented to a subject at multiple locations in the visual field of one or both of the subject's eyes, the resulting set of pupillary responses providing a map of visual function across the visual field of the one or both eyes; (b) the ensemble of visual stimuli is a multifocal stimuli ensemble, the appearance or non-appearance of individual stimuli in the ensemble or other modulations of the stimuli being controlled by statistically independent sequences; and (c) the individual stimuli are each individually balanced such that responses of the pupils to more effective stimuli in the ensemble are reduced to enable larger responses of the pupils to less effective stimuli. (a) the stimuli are visual stimuli presented to a subject at multiple locations in the visual field of one or both of the subject's eyes, the resulting set of pupillary responses providing a map of visual function across the visual field of the one or both eyes; (b) the ensemble of visual stimuli is a multifocal stimuli ensemble, the appearance or non-appearance of individual stimuli in the ensemble or other modulations of the stimuli being controlled by statistically independent sequences; and (c) the individual stimuli are each individually balanced such that responses of the pupils to more effective stimuli in the ensemble are reduced to enable larger responses of the pupils to less effective stimuli.