The weird third eye thing on this alternate sketch of EIB is supposed to be a Polaroid sonar transducer. But much has changed in the last 15 years in the way of robotic rangefinders.
Pokey uses Sharp GPD12 infrared rangers (right) which provide surprisingly accurate results. They determine distance based on the angle of reflection. They're cheap, only $12 each, and they're small, maybe 1.5" x 1/2".
There is a whole family of IR rangefinders, each with a unique (but somewhat limited) distance range. The GPD12's 4"-30" range seemed ideal for measuring distances within the firefighting maze in which Pokey competed.
Modern sonar systems are significantly smaller and also inexpensive, about $30 for something like the Devantech SRF04 Ranger (right). The device is about 2" x 3/4" and includes the driver circuitry on the back of the board.
This particular model uses a separate transducer and receiver. However, you can also get single transducer/receiver models. This device can measure distances from 3cm to 3m!
Of course in the 1990's, tiny cameras with any kind of image processing fell into the realm of impossible or unaffordable.
The CMUcam2+ (left) is able to do high contrast color tracking, all in a 2.25" square package. How times have changed!
There are a number of sources for this gear. I got a sonar ranger from Radio Shack when they were having a sale. I got my Sharp rangers from Acroname (the source of the pictures and info above; no advertising affiliation with the company, I just like 'em).