Discriminative Stimuli

Discriminative Stimuli

My dog is getting older. Her beautiful black and brindle coat now shows a little grey around her muzzle, and her eyes have a trace of haze in them. She’s eleven years old, and at her size that makes her a senior citizen.

We bought her when she was seven months old, from the animal shelter where she had been sent for chewing on the furniture too many times. We were not looking for a Doberman mix. We were looking for maybe a Golden Retriever, or there was a litter of adorable Black Lab/Husky mix puppies that were all spoken for by the time we got there. But this one sat quietly in the midst of barking chaos, and when my wife saw her, she called me to bring the kids. We took the dog for a little walk in the field around the shelter, and while she sniffed at, rolled in, and tried to eat a small mound of frozen horse manure, my family out-voted me. We brought her home, where we discovered that she, despite her fairly large size, considered herself a lapdog.

She is part Greyhound, and she was poetry in motion going after a Frisbee. This past summer, she may have caught one once. She is just not interested in sprinting any more. She does still love to swim, although she does not have the stamina she used to. She’ll swim as long as there is someone else there she needs to protect, but she no longer will sneak out the door and down the path to the lake by herself.

She has a slight heart murmur, we are reminded each time we take her for her annual check-up. Nothing too bad, but something to keep an eye on. I have had to adjust my sleeping schedule on occasion; there will be a few weeks at a time when she needs to wake me up at 3AM to let her outside, or there will be something for me to clean up the next morning.

So tonight, we were out for a walk. It is habit—dogs are great with habit—after supper, I wash the dishes and then we go for our second-to-last evening walk. The skies are dark, with clouds just beginning to file in from the west, and a smell of rain or snow (it is supposed to snow up north, but here we should only get rain); I am walking slowly, eyes skyward, wishing my usual wish upon a star. (What does The Behaviorist think of wishing on stars? That is a topic for another time, I promise.) When I look down, I notice that she is beginning to walk a little funny. A bit bowlegged. This is also something she has only started doing this year. I pick up the pace, and (uncharacteristically, I assure you) run the next 30-40 yards with her, to an appropriate area, where she immediately takes a massive dump. Sadly, her years are playing tricks on her here, too; she is losing control, and may start walking away while…um…not quite finished yet. Poor dog. She is getting old.

For her health and mine, we have begun a new walking regimen. Each morning we set off, walking and gathering our thoughts for the day. We started a few weeks ago with a half hour walk, and are coming closer to an hour by now. We each have our good days and bad days; some days, she limps, others, I do. On days where we both are limping, we take a shorter walk.

For some reason, I am reminded of one of my favorite poems, by one of my favorite poets.

On A Good Dog
by Ogden Nash

O my little pup ten years ago
was arrogant and spry,
Her backbone was a bended bow
for arrows in her eye.
Her step was proud, her bark was loud,
her nose was in the sky,
But she was ten years younger then,
And so, by God was I.

Small birds on stilts along the beach
Rose up with piping cry.
And as they rose beyond her reach
I thought to see her fly.
If natural law refused her wings,
That law she would defy,
for she could do unheard of things,
And so, at times could I.

Ten years ago she split the air
to seize what she could spy;
Tonight she bumps against a chair,
betrayed by milky eye!
She seems to pant, Time up, time up!
My little dog must die,
And lie in dust with Hector’s pup;
So, presently must I.


The science behind it.

Nothing complicated today. A stimulus is anything that can potentially influence a response (“response”, itself, is behaviorese for behavior); there are unconditioned and conditioned eliciting stimuli (in classical conditioning), reinforcing or punishing consequent stimuli (in operant conditioning), and there are discriminative stimuli (again, in operant conditioning), today’s subject.

A discriminative stimulus precedes a response, but does not reflexively elicit the response. Rather, it acts as a signal, alerting the organism (me, you, a rat, a dog…) to the contingencies of reinforcement and punishment. A very simple discriminative stimulus setup might consist of an operant chamber (or Skinner box—I’ll discuss it in more detail in a later post) programmed to deliver a reinforcer of grain if a key is pecked while it is lit, but which will not deliver grain if the key is pecked when it is not lit. A pigeon quickly learns what the “lit key” signal means, and responds appropriately, pecking when the key is lit, but not when it is not.

Discriminative stimuli may signal that a behavior will be reinforced, or that it will be punished. The discriminative stimulus itself does not cause the behavior to occur, but simply signals what will happen if the behavior does occur. There are many discriminative stimuli in our lives: Do you act differently with friends than with parents? If so, these people are discriminative stimuli for different modes of behavior. Are you louder at a ballgame than at a movie? Discriminative stimuli. Traffic signs, storm clouds, red versus green strawberries…discriminative stimuli.

My dog’s gait had changed; her bowlegged scrabbling did not reflexively cause me to run, but it did signal that if we continued walking at the current pace that I would have some serious street-cleaning to do. The discriminative stimulus signaled that walking would be punished, while running would be reinforced.

Her eyes, her lack of stamina, her grey muzzle, her limp…all of these are signals. Walking will be reinforced; so will curling up on the couch. One thing these discriminative stimuli keep saying is “enjoy her now; there may not be many years left.”

I think I’ll pay attention.

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7 Responses to “Discriminative Stimuli”

  1. Kiless Says:

    So what does a behaviourist think of wishing on stars?

    I also have a question – what does a behaviourist, because you must have native population in the area as it’s America and we all know of the reservations and Dances With Wolves and all that, think about superstitions regarding the land that you walk along? Are these things to be respected or tolerated? Is there any akin to a ginko or star wish? Or is that seen as insulting?

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