Pupillary assessment method and apparatus

1. A method for assessing the nervous system of a subject, the method comprising the steps of:

presenting a sequence of selected individual stimuli from at least one stimulus ensemble to the nervous system of a subject 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, the individual stimuli each being 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;

detecting using a sensor 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.

2. A method as claimed in claim 1 wherein the relationship between stimulus intensity and pupillary response size is nonlinear.

3. A method as claimed in claim 1 , wherein nonlinear functions define weights for balancing the pupillary response.

4. A method as claimed in claim 1 wherein different nonlinear functions are used for each individual stimulus in the ensemble.

5. A method as claimed in 1 wherein the nonlinear stimulus/response function is a power function of the form Response=K×stimulus z .

6. A method as claimed in claim 5 further comprising the steps of:

obtaining attenuating weights that are logarithmic for each of the stimuli in the ensemble, the weights being obtained by expressing the response sizes of the stimuli in the ensemble in logarithmic form to provide linear balancing weights; and

multiplying the linear balancing weights to the power z.

7. A method as claimed in claim 6 wherein each individual stimulus in the ensemble is associated with a unique exponent for expression of the attenuating weight for each stimulus.

8. A method as in claim 1 wherein the stimuli are visual stimuli presented to a subject at multiple locations in the visual field one or both of the subjects eyes, the resulting set of pupillary responses providing a map of visual function across the visual field of the one or both eyes.

9. A method as claimed in claim 8 wherein 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 such as intensity, colour (hue) or spatial frequency being controlled by statistically independent sequences.

10. A method as claimed in claim 9 wherein the statistically independent sequences are statistically independent aperiodic pseudorandom sequences.

11. A method as claimed in claim 8 wherein selected individual stimuli of the ensemble are associated with a weighting function, the luminance of the selected stimuli being controlled such that regions of the visual field in which unweighted stimuli evoke large neural responses is decreased.

12. A method as claimed in claim 8 wherein the ensemble of visual stimuli are presented as an ensemble of grating or checkerboard stimuli that are dominated by a range of different spatial frequencies for determination of the visual acuity or spatial frequency tuning of the tested portion of a subject's visual field.

13. A method as claimed in claim 12 wherein the ensemble of stimuli are presented at one or a plurality of spatially resolved locations in the visual field of the subject, such that the pupillary responses to the spatially resolved stimuli are representative of the neural responses to the concurrently presented spatial frequencies thereby to obtain information about the visual acuity and spatial frequency sensitivity of the subject.

14. A method as claimed in claim 8 wherein the visual stimuli are adapted to provide a measure of the distance to objects in the visual field, by presenting stereo disparity cues to each of the subject's eyes, such that the pupillary responses are representative of the function of the accommodative system of the subject's eyes.

15. A method as claimed in claim 8 wherein the ensemble of visual stimuli is a first ensemble for presentation to one eye of the subject, the method further comprising:

concurrently presenting a second ensemble of unique visual stimuli to the other eye of the subject;

recording the pupillary responses of a selected one of the two retinas;

characterising the pupillary response of the retina associated with the recorded pupil by the direct pupil response; and

characterising the pupillary response of the other retina by the consensual response of the recorded pupil.

16. A method as in claim 1 wherein the visual stimuli at one or several locations alternate between one of a number of stimulus conditions.

17. A method as claimed in claim 16 wherein the stimulus conditions are selected from the group consisting of stimulus luminance level, stimulus colour or hue, and wherein the stimulus conditions for each stimulus in the ensemble is each controlled by a unique statistically independent sequence such that the pupillary responses are representative of the neural responses affected by a stimulus space spanned by those stimulus conditions.

18. A method as claimed in claim 1 wherein the stimuli in the ensemble are adapted such that the pupillary responses evoked by said stimuli are substantially unsaturated.

19. A method as claimed in claim 1 wherein the ensemble of stimuli is an ensemble of auditory stimuli.

20. A method as claimed in claim 1 wherein the ensemble of stimuli evoke particular emotions, or modulate the mental health of a subject, the method comprising recording the pupillary response of the subjected evoked by the ensemble of stimuli; and characterising the function of those neural mediated emotional or mental health mechanisms of the subject from the recorded responses.

21. A method as claimed in claim 1 wherein the ensemble of stimuli is an ensemble of different drugs or other chemical substances, or difference dosages of a drug or substance, that are known to affect the function of the pupils.

22. A method as claimed in claim 1 wherein the ensemble of stimuli comprises a mixture of visual, accommodative, auditory, emotional, or chemical stimuli.

23. A method as claimed in claim 1 , wherein the stimuli are controlled by statistically independent sequences with a selected mean inter-stimulus symbol interval period.

24. A method as claimed in claim 23 wherein the mean inter-stimulus interval period is selected to be in the range of about 0.25 s/region to about 16 s/region.

25. A method as claimed in claim 24 wherein the mean inter-stimulus interval period is selected to be either about 1 s/region or about 4 s/region.

26. A system for assessing the nervous system of a subject, the system comprising:

means for generating sequences of stimuli from at least one stimulus ensemble adapted to evoke pupillary responses in at least one pupil of the subject, said stimulus ensemble comprising a plurality of individual stimuli, the stimulus generation means individually determining at least one weighting function for each of the individual stimuli in the stimulus ensemble such that the pupillary responses to individual stimuli in the ensemble are balanced according to the strength of the neural responses evoked by the individual stimuli, the individual stimuli each being 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;

display means for presenting said sequence of balanced stimuli to the nervous system of a subject for the generation of pupillary responses in at least one pupil of the subject;

a sensor for detecting the pupillary responses of at least one pupil evoked by the sequence of balanced stimuli; and

a processor for recording and relating the detected pupillary responses to relate them to the function of the subject's neural responses to at least two of the individual stimuli of the ensemble.

27. A system as claimed in claim 26 further comprising a database of recorded data, the recorded data comprising information on at least one or more of:

the strength or mean strength of the neural responses evoked in at least one subject by the individual stimuli;

the strength or mean strength of the pupillary responses evoked in at least one subject by the individual stimuli;

wherein the stimulus generation means determines the at least one weighting function for each of the individual stimuli from an analysis of the recorded data.

28. A system as claimed in claim 27 wherein the analysis of the recorded data for determination of the weighting function(s) provides a relationship between the intensity of the individual stimuli and pupillary responses evoked therefrom in the form of one or more nonlinear functions.

29. A system as claimed in claim 28 wherein the nonlinear stimulus/response function is a power function of the form Response=K×stimulus z .

30. A system as claimed in claim 29 wherein each individual stimulus in the ensemble is associated with a unique exponent for expression of the attenuating weight for each stimulus.

31. A system as claimed in claim 26 wherein the stimuli are visual stimuli presented to a subject at multiple locations in the visual field 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.

32. A system as claimed in claim 26 , wherein the means for generating sequences of stimuli is adapted to present the statistically independent sequences of stimuli with a selected mean inter-stimulus symbol interval period.

33. A system as claimed in claim 32 wherein the means for generating sequences of stimuli is adapted to selectively present the statistically independent sequences of stimuli with a mean inter-stimulus interval period wherein the mean inter-stimulus interval period is selected to be in the range of about 0.25 s/region to about 16 s/region.

34. A system as claimed in claim 33 wherein the mean inter-stimulus interval period is selected to be either about 1 s/region or about 4 s/region.

35. A system as claimed in claim 32 wherein the statistically independent sequences are statistically independent aperiodic pseudorandom sequences.