The document describes an experiment using a Broca's pupillometer to demonstrate the dilation and constriction responses of pupils in reaction to light. By observing blurred images through pinholes while covering one eye, it shows that the iris of one eye responds to the light entering the other eye, indicating a connection between their responses. Paul Broca's background in studying the relationship between brain regions and specific functions is also mentioned.

1. 073 THE IRIS DIAPHRAGM
Iris acts like the diaphragm of a camera, dilating and constricting the pupil to
allow light of differing intensities into the eye. The experiment describes how
the dilation and constriction responses of one pupil are geared to the other.
MATERIAL REUIRED
Card board > 5cm2
White paper
Pin
A pair of scissors
Ruler with cm measurements
Pencil.

2. In the centre of a piece of thin card
about 5 cm2 make a pattern of fine
pin-holes as shown in figure. Trim the
corners off the card. This is called a
Broca's pupillometer.
Close one eye and hold the card very
close to the other, actually touching
your face, and look through the pin-holes
at a brightly lit sheet of plain
white paper.
PINHOLES
3mm
4mm
5mm
BROCA’S PUPILLOMETER
APPEARANCE
OF PINHOLES
OBS. ERVE?
The pin-holes appear as a pattern of unfocussed light discs.
Some of the discs appear to overlap, others will appear to
be separated

3. Now concentrate on a pair that is nearly touching but not overlapping. While
still concentrating on this pair of discs with one eye, open the other.
Describe what you observe now.
The blurred images of the pin-holes suddenly become smaller and sharper.
How does this happen?
When the closed eye is suddenly opened, the extra light entering causes the
irises of both eyes to reduce the size of the pupils and as a result, the blurred
images of the pin-holes become smaller and sharper.
What does this prove?
This shows that the response of one eye is geared to the other.
Did you realize that holding the card very close to your face actually cuts
most of the light falling on the eye and makes the pupil dilate?
Paul Broca (1824-1880) was a French surgeon and anthropologist who
studied the effect on behaviour of brain lesions. He located the area of the
brain concerned with speech and thus was the first person to associate brain
regions with specific functions.

4. PINHOLE
CARD
NARROW- PUPIL - WIDE
IRIS
REFRACTION AT LENS
BLURRED DISCS OF LIGHT – USING ONE
EYE IN DIM LIGHT DILATES PUPIL
RETINA
SMALLER DISCS THAT SEEM TO MOVE APART
– PUPILS CONSTRICT AS A REPONSE TO
BRIGHT LIGHT