.......... is a decrease in the response to an ongoing stimulus.

Options

A. perception
B. visual accommodation
C. sensory adaptation
D. both (b) and (c)

Explanation

### Step-by-Step Solution:

1. **Understanding the Question**: The question asks for a term that describes a decrease in response to an ongoing stimulus. This indicates that when a stimulus is constant, the body's response to it diminishes over time.

2. **Identifying the Concept**: The phenomenon where the sensory system becomes less responsive to a constant stimulus is known as "sensory adaptation." This is a key concept in neural control and coordination.

3. **Explaining Sensory Adaptation**: Sensory adaptation occurs when sensory receptors decrease their response to a constant stimulus. For example, when you sit on a chair, you initially feel the pressure of the chair against your skin, but after a while, you may not notice it at all. This is because the sensory neurons adapt to the constant pressure and reduce their signaling.

4. **Example of Sensory Adaptation**: Consider the example of standing on a table. When you first make contact with the table, your skin's sensory neurons are activated, and you feel the surface. However, after a few seconds, the sensation diminishes, and you may no longer consciously feel the table against your skin. This illustrates how the body adapts to ongoing stimuli.

5. **Conclusion**: Therefore, the term that fits the description of a decrease in response to an ongoing stimulus is "sensory adaptation."

### Final Answer:
**Sensory adaptation** is a decrease in the response to an ongoing stimulus.

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