Stein et al., 1989

Behavioral Indices of Multisensory Integration: Orientation to Visual Cues is Affected by Auditory Stimuli

1. Big question (why this paper exists)

At the time, most multisensory work showed single neurons in the superior colliculus (SC) integrating vision and sound.

This paper asks:
Do those same “rules” show up in real behavior?

Superior colliculus: a midbrain structure involved in orienting—turning your eyes, head, or body toward something. 

2. What they did 

They trained cats to orient toward lights and sounds placed at different positions around them.

• Visual stimulus: a small LED light

• Auditory stimulus: a brief noise burst

• Behavioral measure: did the cat move toward the correct location?

They tested three paradigms (this becomes crucial for the figures). 

3. Figure walkthrough

Figure 1 – The task setup

• Spatially coincident condition:
  Light and sound come from the same place.

• Spatially disparate condition:
  Light comes from one place, sound from another (e.g., 60° apart).

• Spatial resolution condition:
  Sound is gradually shifted farther away from the visual target.

👉 Lay explanation:
This is a controlled way to test whether the brain binds signals based on space.

Figure 2 – Multisensory enhancement

This shows percent correct responses.

• Visual alone = okay

• Auditory alone = okay

• Auditory + visual together = much better

Technical term: Multisensory enhancement
Plain meaning: performance improves more than expected when senses are combined.

Key teaching point:
The improvement is bigger than either sense alone, even at peripheral locations.

Figure 3 – Inverse effectiveness

This is a classic figure students will see again later.

• When single cues are weak, multisensory benefit is largest

• When cues are already strong, the benefit shrinks

Inverse effectiveness: multisensory integration is strongest when individual cues are poor.

Lay explanation: The brain combines signals most aggressively when it’s unsure.

Figure 4 – Beyond probability

They compare actual performance to a probability summation model.

Probability summation: improvement happens just because there are two chances to detect something.

The real performance exceeds this prediction.

“This isn’t just two senses racing—it’s the brain combining them.”

Figures 5–7 – Spatial mismatch suppresses behavior

When sound and light come from different locations:

• Performance drops below visual alone

• This is called multisensory depression

Multisensory depression: mismatched cues actively interfere with each other.

Crucial insight:

The brain doesn’t just fail to integrate—it suppresses conflicting information.

4. Take-home message

The same spatial rules seen in single SC neurons appear at the behavioral level.

Multisensory integration is not abstract—it directly shapes how organisms act.