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The saccadometer

	The saccadometer is a miniaturised, portable device for recording saccadic responses to visual stimuli. It consists of a transducer, that is worn on the head and measures the subject's eye movements as well as generating the stimuli, and a control unit joined to the transducer, that runs the experiments and stores the results.
	Eye movements are measured non-invasively using infra-red reflection, and miniature lasers mounted on the transducer project small stimuli on to any convenient surface in front of the subject. Because these stimuli move with the head, no head restraint of any kind is needed , and the subject can sit comfortably in a chair, or lie on a bed lookng at the ceiling. The system requires virtually no setting up: the transducer rests securely on the bridge of the nose and is automatically self-calibrating.
	The saccadometer performs an entire experiment without operator intervention: a run of 100 saccades typically takes about three minutes. In the simplest saccadometer, the target steps randomly to the left or right, with a randomised foreperiod; when the resultant saccade is detected the next trial begins automatically. More advanced saccadometers can be programmed to carry out more complex tasks, with colour-cuing for Go/No-go and countermanding tasks. Most saccadometers can also be used to measure manual response times, using the buttons on the controller and its LEDs.

After collection, data can be downloaded via an optic fibre/USB link to a computer for analysis, using the software that is provided with the system. The application LatencyMeter analyses the individual saccadic position and velocity profiles from a session or group of sessions, and can automatically detect and eliminate individual trials that are contaminated by blinks, head movements, or inattention. It tabulates and displays both latency and velocity data, and this can be exproted to th second application, SPIC, for more detailed analysis of the latency distributions. SPIC carries out a variety of statistical tests, and will also run simulations of models set up by the user, as well as creating and storing reciprobit plots of distributions. The gallery below shows some typical screenshots from LatencyMeter and SPIC.

	LatencyMeter: Sets of position and velocity profiles from a number of trials, automatically triaged to eliminate aberrant records
	LatencyMeter: Sets of saccadic responses showing variation in latency, with tabulation of results at left.
	SPIC: Panel for selection of groups of responses, showing preliminary raw histogram at bottom right
	SPIC: Panel for statistical analysis and fitting of latency distributions, showing results of modelling at left and the corresponding reciprobit plots at right.
	SPIC: Panel for creating models and running simulations. The main panel has a text description of the model, shown graphically at right; above, result of a single trial.
	SPIC: Logging panel, to which the results of all tests and procedures are automatically pasted. Below, examples of 3D plots of the LATER parameters for particular groups.

It is important to note the limitations of this device: it is what it says, a saccadometer. What it reports is the average, cyclopean, position of the two eyes in the horizontal plane. If you want to study vertical movements, or vergence, you need something different. However, the saccadometer head can be connected to an oculometry interface box, that generates a robust anlogue signal representing horizontal eye position, in real time. An ideal arrangement, for more advanced laboratory investigations, is to connect this to a ViSaGe system (Cambridge Research Systems, for which a specific interface for SPIC is already provided that implements real-time experiments on saccadic responses to highly complex visual targets and protocols to be performed. It will also allow experiments on smooth pursuit to be performed.