Similar terms - I am no expert of course - any thoughts on differences between the two?

Low excitement threshold, to me, just tells me the dog will react quickly to stimuli. It doesn't tell how it will react. Sharp tells me the dog will act with aggression. How much agression
depends on the level of sharpness in the dog.

Another explination. All three of my terriers will react quickly to stimuli. They have a low excitement threshold. They are all very aware of their suroundings. The difference with the JRT, is he is a sharp dog and will easily get agressive. He is bordering on being a sharp, shy dog. In otherwords, he will bite out of fear. The two Borders will react quickly to any stimuli, but would never bite(under most all circumstances)

IMHO, I'm not an expert either, Most sharp dogs have a low excitement threshold. Not all dogs with a low excitement threshold are sharp. A dog with a great prey drive has a low excitement threshold eg the ball, sleeve, etc. They may not be sharp at all, due to a lack of defence. A lab has a low excitement threshold, but is rarely sharp.

Boy I guess I've no idea. I've always thought that a sharp dog was one that was very leary of strangers. Someone walks up to it to pet it and the dog sort of backs away slow non agressive but not shy either then when you let it know all is ok with this stranger the dog becomes friendly. Genes not a tought thing.

IMO the term sharp is used to denote different things by different people.

A lot of terms used in this feild are not very exact. We talk about prey and defence as the main drives. That's kinda like describing what a human does and why with the Freud's concepts of eros (drive to love and reproduce)and Thanatos (drive to dye).

Dogs are called sharp when they act quickly with aggression. What that doesn't tell us is why. Are there appropriate cues.

Ussually the concepts of sharpness (The dogs aggressive behavior "R") and a low excitment threshold (Amount of stimulus needed to evoke a response SD1) go hand and hand. But we are talking about two different aspects or qualities of the dog. Theoretically you could have a very high threshold (takes a significant stimulus like a man raising a bat to trigger the dog) and the dog could still be sharp (quick to react after the stimulus threshold is reached). On the other hand you could have a very low threshold (person raises hand for hand shake).

I think Eric is on target and posted this statement/question.

Dogs are called sharp when they act quickly with aggression. What that doesn't tell us is why. Are there appropriate cues?

To answer: Yes.

For a better explanation… Please read on.

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A warning for new dog owners and trainers: Dog training is not complex. Behavior and the study of behavior can be. You do not need to have intense knowledge in the science of behavior and theory to train your dog though it is helpful at times to learn the basics. The following post is for any and all who are interested in the nuts and bolts of training and behavior.
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When Eric posted: Theoretically you could have a very high threshold (takes a significant stimulus like a man raising a bat to trigger the dog) and the dog could still be sharp (quick to react after the stimulus threshold is reached).

Sharpness is a reflexive action and in this case it involves social interaction. (real or perceived)

When we study behavior and the sharpness of a dog who is exposed to a particular stimulus like a person raising a bat and the dog reacting with aggression is at the highest level of reflexive behavior know as Modal Action Patterns (MAP)

The traditional behavior model, which I think does not complete the picture, would look like this:

Increasing Stimulus --- response 1 ---- response 2 ----- response 3 ---- response 4 and so on…
Example:

Simple
Man ----to---- man raising hand --- growl/whine --- move ---- fight
Man----to----- man raising hand --- growl/whine --- move ---- escape
Or
Man----to----- man raising hand --- move ---- escape
Man----to----- man raising hand --- growl/whine --- move ---- escape
Man----to----- man raising hand --- growl/whine --- move ---- escape

Again, this is at the end of the “pressure” that was internalized since the dog became aware of the man.

How MAPs fit into the picture is explained by adding another levels of complexity to reflexes, which has already been defined by science. This level is known as an Interacting Reflexive Arc and it explains the “pressure building” that takes place before a strong biologically influenced response like fight or flight takes place.

An example of internalized pressure using the standard Interacting Reflexive Arc model would looks like this:

Stimulus 1 to response 1 --- ignore or on to ---- ignore or on to ----- stimulus 2 response 2 ----- on so on up to a biologically influenced behavior based in survival (fight or flight)

Here is where we enter a new door in thought, as the traditional explanation currently accepted would end with the Interacting Reflexive Arc that evolves to the trigger (MAP) to Biologically influenced response for survival if any.

I felt a few pieces needed to be added to this equation (if only to be reamed by Van Camp about it) – just kidding Robert.

The threshold window I made to help me think more clearly about the internal pressures (Interactive Reflexive Arc) that lead to (trigger) a reflexive behavior in dogs is as follows:

<img src="/ubbthreads/images/graemlins/smile.gif" alt="" /> Stimulus1---to Response1

(1) Selection - Determining the existence of cue or cues
(2) Division - Cognitive selection against temperament within the dog
(3) Alertness – Focus or ignore or submission
(4) Trigger - (response if any) Example response: whines
:rolleyes: <img src="/ubbthreads/images/graemlins/mad.gif" alt="" />

<img src="/ubbthreads/images/graemlins/smile.gif" alt="" /> Stimulus 2 ---- to ---- response 2
(1) Selection - Determining the existence of cue or cues
(2) Division - Cognitive selection against temperament within the dog
(3) Alertness – Focus or ignore or submission
(4) Trigger - (response if any)
Example response: barks in defense
:rolleyes: <img src="/ubbthreads/images/graemlins/mad.gif" alt="" />

....And so on until the threshold hits top pressure and a fight or flight or submission reaction happens.

The degree of this arc and all its components are translated into sharpness if as Eric stated if the dog ‘exhibits an aggressive behavior "R" and a low excitement threshold’ exist.

Understand this example applies only to the given scenario. While it is an indication of future responses the variables would be different. Variables like sensitization, Habituation and environmental conditions to name a few. Habituation effects (and sensitization effects) are temporary and therefore are not true learned behaviors so like the environment their strength and influence can and will vary.

Though the things that lead up to a response will vary, I think they follow along these lines of thought. The example of a man raising a stick scenario to help define sharpness in this post is a decent reference to begin with.