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Visual Occlusion Instrument (George Kelk)

Engineering Psychology

The instrument consists of two components: a visor assembly that is connected by a long electrical cord to a main control unit.

The visor assembly is made primarily of wood and aluminum. On either side of the rear of the visor is a slot that is presumably used to attach a headband for securing the visor to a subject’s head. The front of the visor has two slots for the subject to look through. Adjacent to each slot is an electrically controlled pivoting shutter whose surface is painted black. Set screws above and below each shutter limit the shutters’ travel.

The control unit is a large metal enclosure with a grey anodized finish. The front of the unit is a console consisting of several dials and switches that permit the right and left shutter to be controlled independently. The front part of the console is removable. There is a hinged panel at the top of the console that opens to reveal electrical components, including several vacuum tubes, inside the console. There is a metal handle on either side of the instrument.

An accompanying manual, created by George Kelp Limited, provides technical information and electrical schematics.

Accession Number: 2014.ep.4

Alternative Name:

Primary Materials: Steel, Aluminum, Glass, Wood, Plastic.


A plaque on the control unit’s front panel reads contains the following information: “George Kelk LTD. Toronto Canada”, “Light Shutter”, [Model Number] “P-42”.

Typewritten labels have been pasted to the electrical board indicating the necessary voltage and model of most vacuum tubes.

Dimensions (cm):

Control Unit: Height = 27.6, Width = 54, Length = 39; Head Assembly: Height = 9.7, Width = 7.2, Length = 22.8


This instrument is used to periodically block the subject’s view over intervals that are adjustable for each eye.

Such visual occlusion instruments are used in research related to visual perception and psychomotor behaviour, as well as ergonomic testing and evaluation. As this instrument was developed by the Defence Research Medical Laboratory (DRML) in the 1950s, it was likely used in the development and optimization of human-machine interfaces. In such research, by periodically interrupting the view of a task, and measuring the subject’s reaction, one can evaluate its relative difficulty.


The rubber coating on the two main electrical wires is brittle and already cracked in places. The wire connecting to the Head Assembly has begun to fray leaving the wires exposed. The electrical board is covered in thick dust and other small particles. The previous repairs to the left “Off/Run/On” switch have left green tape visible and the switch is still loose; a piece has broken off of the right “Freq. Range” dial; there is residue from masking tape in the centre of the front panel; the top panel is dented in the centre; there are a few minor scuffs and scratches primarily on the front panel and right side of the Control Unit box; and there are chips and scratches on the shutters of the Head Assembly (one large chip on the right eye shutter).

NOTE: The front console assembly is unsecured and will fall out if the enclosure if it is tilted.

Associated Instruments:


George Kelk Limited, 130 Willowdale Ave., Willowdale, On.

Date of Manufacture: c. 1958


This artifact was created for the Defence Research Medical Laboratory (DRML) of the Department of National Defence, located at 1130 Sheppard Ave. W., Toronto, ON, by George Kelk Limited, at some point in the mid-to-late 1950s. An invoice included with the instrument’s paper manual indicates that the instrument was returned by Kelk to DRML on June 12 of 1958 after a modification.

The paper manual is stamped “Department of Industrial Engineering// University of Toronto// Toronto// Ontario, Canada” in blue on the cover.

The artifact was gathered from the office of Prof. Paul Milgram of the University of Toronto Department of Mechanical and Industrial Engineering on October 9, 2012.

Additional Information and References:

Historical Notes:

  • Donated to UTSIC