A brain computer interface system, comprising: a display unit for displaying image data, the image data including at least one object, the display unit further outputting a respective visual stimulus (311, 311') to correspond to one or more of said objects, a stimulus generator for generating the or each visual stimulus with a corresponding characteristic modulation; a neural signal capture device configured to capture neural signals associated with a user; and an interfacing device operatively coupled to the neural signal capture device and the stimulus generator, the interfacing device being configured to: receive the neural signals from the neural signal capture device; determine a strength of components of the neural signals having a property associated with the respective characteristic modulations of the or each visual stimulus; determine which of the at least one visual stimuli is associated with an object of focus of the user based on the neural signals, the object of focus being inferred from the presence and/or relative strength of the components of the neural signals having a property associated with the characteristic modulation of the visual stimulus; and characterised in that the interfacing device being further configured to cause the stimulus generator to generate the visual stimulus as a compound visual stimulus comprising at least a first portion with a first characteristic modulation and a first visual property and a second portion with a second characteristic modulation and a second visual property, the second visual property being distinct from the first visual property, wherein the first portion and the second portion are overlaid at substantially the same location. a display unit for displaying image data, the image data including at least one object, the display unit further outputting a respective visual stimulus (311, 311') to correspond to one or more of said objects, a stimulus generator for generating the or each visual stimulus with a corresponding characteristic modulation; a neural signal capture device configured to capture neural signals associated with a user; and an interfacing device operatively coupled to the neural signal capture device and the stimulus generator, the interfacing device being configured to: receive the neural signals from the neural signal capture device; determine a strength of components of the neural signals having a property associated with the respective characteristic modulations of the or each visual stimulus; determine which of the at least one visual stimuli is associated with an object of focus of the user based on the neural signals, the object of focus being inferred from the presence and/or relative strength of the components of the neural signals having a property associated with the characteristic modulation of the visual stimulus; and characterised in that the interfacing device being further configured to cause the stimulus generator to generate the visual stimulus as a compound visual stimulus comprising at least a first portion with a first characteristic modulation and a first visual property and a second portion with a second characteristic modulation and a second visual property, the second visual property being distinct from the first visual property, wherein the first portion and the second portion are overlaid at substantially the same location. receive the neural signals from the neural signal capture device; determine a strength of components of the neural signals having a property associated with the respective characteristic modulations of the or each visual stimulus; determine which of the at least one visual stimuli is associated with an object of focus of the user based on the neural signals, the object of focus being inferred from the presence and/or relative strength of the components of the neural signals having a property associated with the characteristic modulation of the visual stimulus; and characterised in that the interfacing device being further configured to cause the stimulus generator to generate the visual stimulus as a compound visual stimulus comprising at least a first portion with a first characteristic modulation and a first visual property and a second portion with a second characteristic modulation and a second visual property, the second visual property being distinct from the first visual property, wherein the first portion and the second portion are overlaid at substantially the same location.